Datasets:
Tasks:
Text Generation
Modalities:
Text
Sub-tasks:
language-modeling
Languages:
English
Size:
100K - 1M
License:
File size: 106,094 Bytes
4365a98 |
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690 691 692 693 694 695 696 697 698 699 700 701 702 703 704 705 706 707 708 709 710 711 712 713 714 715 716 717 718 719 720 721 722 723 724 725 726 727 728 729 730 731 732 733 734 735 736 737 738 739 740 741 742 743 744 745 746 747 748 749 750 751 752 753 754 755 756 757 758 759 760 761 762 763 764 765 766 767 768 769 770 771 772 773 774 775 776 777 778 779 780 781 782 783 784 785 786 787 788 789 790 791 792 793 794 795 796 797 798 799 800 801 802 803 804 805 806 807 808 809 810 811 812 813 814 815 816 817 818 819 820 821 822 823 824 825 826 827 828 829 830 831 832 833 834 835 836 837 838 839 840 841 842 843 844 845 846 847 848 849 850 851 852 853 854 855 856 857 858 859 860 861 862 863 864 865 866 867 868 869 870 871 872 873 874 875 876 877 878 879 880 881 882 883 884 885 886 887 888 889 890 891 892 893 894 895 896 897 898 899 900 901 902 903 904 905 906 907 908 909 910 911 912 913 914 915 916 917 918 919 920 921 922 923 924 925 926 927 928 929 930 931 932 933 934 935 936 937 938 939 940 941 942 943 944 945 946 947 948 949 950 951 952 953 954 955 956 957 958 959 960 961 962 963 964 965 966 967 968 969 970 971 972 973 974 975 976 977 978 979 980 981 982 983 984 985 986 987 988 989 990 991 992 993 994 995 996 997 998 999 1000 1001 1002 1003 1004 1005 1006 1007 1008 1009 1010 1011 1012 1013 1014 1015 1016 1017 1018 1019 1020 1021 1022 1023 1024 1025 1026 1027 1028 1029 1030 1031 1032 1033 1034 1035 1036 1037 1038 1039 1040 1041 1042 1043 1044 1045 1046 1047 1048 1049 1050 1051 1052 1053 1054 1055 1056 1057 1058 1059 1060 1061 1062 1063 1064 1065 1066 1067 1068 1069 1070 1071 1072 1073 1074 1075 1076 1077 1078 1079 1080 1081 1082 1083 1084 1085 1086 1087 1088 1089 1090 1091 1092 1093 1094 1095 1096 1097 1098 1099 1100 1101 1102 1103 1104 1105 1106 1107 1108 1109 1110 1111 1112 1113 1114 1115 1116 1117 1118 1119 1120 1121 1122 1123 1124 1125 1126 1127 1128 1129 1130 1131 1132 1133 1134 1135 1136 1137 1138 1139 1140 1141 1142 1143 1144 1145 1146 1147 1148 1149 1150 1151 1152 1153 1154 1155 1156 1157 1158 1159 1160 1161 1162 1163 1164 1165 1166 1167 1168 1169 1170 1171 1172 1173 1174 1175 1176 1177 1178 1179 1180 1181 1182 1183 1184 1185 1186 1187 1188 1189 1190 1191 1192 1193 1194 1195 1196 1197 1198 1199 1200 1201 1202 1203 1204 1205 1206 1207 1208 1209 1210 1211 1212 1213 1214 1215 1216 1217 1218 1219 1220 1221 1222 1223 1224 1225 1226 1227 1228 1229 1230 1231 1232 1233 1234 1235 1236 1237 1238 1239 1240 1241 1242 1243 1244 1245 1246 1247 1248 1249 1250 1251 1252 1253 1254 1255 1256 1257 1258 1259 1260 1261 1262 1263 1264 1265 1266 1267 1268 1269 1270 1271 1272 1273 1274 1275 1276 1277 1278 1279 1280 1281 1282 1283 1284 1285 1286 1287 1288 1289 1290 1291 1292 1293 1294 1295 1296 1297 1298 1299 1300 1301 1302 1303 1304 1305 1306 1307 1308 1309 1310 1311 1312 1313 1314 1315 1316 1317 1318 1319 1320 1321 1322 1323 1324 1325 1326 1327 1328 1329 1330 1331 1332 1333 1334 1335 1336 1337 1338 1339 1340 1341 1342 1343 1344 1345 1346 1347 1348 1349 1350 1351 1352 1353 1354 1355 1356 1357 1358 1359 1360 1361 1362 1363 1364 1365 1366 1367 1368 1369 1370 1371 1372 1373 1374 1375 1376 1377 1378 1379 1380 1381 1382 1383 1384 1385 1386 1387 1388 1389 1390 1391 1392 1393 1394 1395 1396 1397 1398 1399 1400 1401 1402 1403 1404 1405 1406 1407 1408 1409 1410 1411 1412 1413 1414 1415 1416 1417 1418 1419 1420 1421 1422 1423 1424 1425 1426 1427 1428 1429 1430 1431 1432 1433 1434 1435 1436 1437 1438 1439 1440 1441 1442 1443 1444 1445 1446 1447 1448 1449 1450 1451 1452 1453 1454 1455 1456 1457 1458 1459 1460 1461 1462 1463 1464 1465 1466 1467 1468 1469 1470 1471 1472 1473 1474 1475 1476 1477 1478 1479 1480 1481 1482 1483 1484 1485 1486 1487 1488 1489 1490 1491 1492 1493 1494 1495 1496 1497 1498 1499 1500 1501 1502 1503 1504 1505 1506 1507 1508 1509 1510 1511 1512 1513 1514 1515 1516 1517 1518 1519 1520 1521 1522 1523 1524 1525 1526 1527 1528 1529 1530 1531 1532 1533 1534 1535 1536 1537 1538 1539 1540 1541 1542 1543 1544 1545 1546 1547 1548 1549 1550 1551 1552 1553 1554 1555 1556 1557 1558 1559 1560 1561 1562 1563 1564 1565 1566 1567 1568 1569 1570 1571 1572 1573 1574 1575 1576 1577 1578 1579 1580 1581 1582 1583 1584 1585 1586 1587 1588 1589 1590 1591 1592 1593 1594 1595 1596 1597 1598 1599 1600 1601 1602 1603 1604 1605 1606 1607 1608 1609 1610 1611 1612 1613 1614 1615 1616 1617 1618 1619 1620 1621 1622 1623 1624 1625 1626 1627 1628 1629 1630 1631 1632 1633 1634 1635 1636 1637 1638 1639 1640 1641 1642 1643 1644 1645 1646 1647 1648 1649 1650 1651 1652 1653 1654 1655 1656 1657 1658 1659 1660 1661 1662 1663 1664 1665 1666 1667 1668 1669 1670 1671 1672 1673 1674 1675 1676 1677 1678 1679 1680 1681 1682 1683 1684 1685 1686 1687 1688 1689 1690 1691 1692 1693 1694 1695 1696 1697 1698 1699 1700 1701 1702 1703 1704 1705 1706 1707 1708 1709 1710 1711 1712 1713 1714 1715 1716 1717 1718 1719 1720 1721 1722 1723 1724 1725 1726 1727 1728 1729 1730 1731 1732 1733 1734 1735 1736 1737 1738 1739 1740 1741 1742 1743 1744 1745 1746 1747 1748 1749 1750 1751 1752 1753 1754 1755 1756 1757 1758 1759 1760 1761 1762 1763 1764 1765 1766 1767 1768 1769 1770 1771 1772 1773 1774 1775 1776 1777 1778 1779 1780 1781 1782 1783 1784 1785 1786 1787 1788 1789 1790 1791 1792 1793 1794 1795 1796 1797 1798 1799 1800 1801 1802 1803 1804 1805 1806 1807 1808 1809 1810 1811 1812 1813 1814 1815 1816 1817 1818 1819 1820 1821 1822 1823 1824 1825 1826 1827 1828 1829 1830 1831 1832 1833 1834 1835 1836 1837 1838 1839 1840 1841 1842 1843 1844 1845 1846 1847 1848 1849 1850 1851 1852 1853 1854 1855 1856 1857 1858 1859 1860 1861 1862 1863 1864 1865 1866 1867 1868 1869 1870 1871 1872 1873 1874 1875 1876 1877 1878 1879 1880 1881 1882 1883 1884 1885 1886 1887 1888 1889 1890 1891 1892 1893 1894 1895 1896 1897 1898 1899 1900 1901 1902 1903 1904 1905 1906 1907 1908 1909 1910 1911 1912 1913 1914 1915 1916 1917 1918 1919 1920 1921 1922 1923 1924 1925 1926 1927 1928 1929 1930 1931 1932 1933 1934 1935 1936 1937 1938 1939 1940 1941 1942 1943 1944 1945 1946 1947 1948 1949 1950 1951 1952 1953 1954 1955 1956 1957 1958 1959 1960 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 2023 2024 2025 2026 2027 2028 2029 2030 2031 2032 2033 2034 2035 2036 2037 2038 2039 2040 2041 2042 2043 2044 2045 2046 2047 2048 2049 2050 2051 2052 2053 2054 2055 2056 2057 2058 2059 2060 2061 2062 2063 2064 2065 2066 2067 2068 2069 2070 2071 2072 2073 2074 2075 2076 2077 2078 2079 2080 2081 2082 2083 2084 2085 2086 2087 2088 2089 2090 2091 2092 2093 2094 2095 2096 2097 2098 2099 2100 2101 2102 2103 2104 2105 2106 2107 2108 2109 2110 2111 2112 2113 2114 2115 2116 2117 2118 2119 2120 2121 2122 2123 2124 2125 2126 2127 2128 2129 2130 2131 2132 2133 2134 2135 2136 2137 2138 2139 2140 2141 2142 2143 2144 2145 2146 2147 2148 2149 2150 2151 2152 2153 2154 2155 2156 2157 2158 2159 2160 2161 2162 2163 2164 2165 2166 2167 2168 2169 2170 2171 2172 2173 2174 2175 2176 2177 2178 2179 2180 2181 2182 2183 2184 2185 2186 2187 2188 2189 2190 2191 2192 2193 2194 2195 2196 2197 2198 2199 2200 2201 2202 2203 2204 2205 2206 2207 2208 2209 2210 2211 2212 2213 2214 2215 2216 2217 2218 2219 2220 2221 2222 2223 2224 2225 2226 2227 2228 2229 2230 2231 2232 2233 2234 2235 2236 2237 2238 2239 2240 2241 2242 2243 2244 2245 2246 2247 2248 2249 2250 2251 2252 2253 2254 2255 2256 2257 2258 2259 2260 2261 2262 2263 2264 2265 2266 2267 2268 2269 2270 2271 2272 2273 2274 2275 2276 2277 2278 2279 2280 2281 2282 2283 2284 2285 2286 2287 2288 2289 2290 2291 2292 2293 2294 |
(* ========================================================================= *)
(* Calculation with real numbers (Boehm-style but by inference). *)
(* ========================================================================= *)
needs "Library/transc.ml";;
let REAL_SUB_SUM0 = prove
(`!x y m. sum(0,m) x - sum(0,m) y = sum(0,m) (\i. x i - y i)`,
CONV_TAC(ONCE_DEPTH_CONV SYM_CONV) THEN
GEN_TAC THEN GEN_TAC THEN INDUCT_TAC THEN
ASM_REWRITE_TAC[sum] THEN
REAL_ARITH_TAC);;
let REAL_MUL_RSUM0 = prove
(`!m c x. c * sum(0,m) x = sum(0,m) (\i. c * x(i))`,
INDUCT_TAC THEN
ASM_REWRITE_TAC[sum; REAL_MUL_RZERO; REAL_ADD_LDISTRIB]);;
let REAL_ABS_LEMMA = prove
(`!a b n. (&a pow n) * abs b = abs((&a pow n) * b)`,
REWRITE_TAC[REAL_ABS_MUL; REAL_ABS_POW; REAL_ABS_NUM]);;
let REAL_ABS_LEMMA1 = prove
(`!a b. &a * abs b = abs(&a * b)`,
REWRITE_TAC[REAL_ABS_MUL; REAL_ABS_NUM]);;
let REAL_ABS_TRIANGLE_LEMMA = prove
(`!u x y z. abs(x - y) + abs(z - x) < u ==> abs(z - y) < u`,
REAL_ARITH_TAC);;
let REAL_MONO_POW2 = prove
(`!m n. m <= n ==> &2 pow m <= &2 pow n`,
REPEAT GEN_TAC THEN REWRITE_TAC[LE_EXISTS] THEN
DISCH_THEN(X_CHOOSE_THEN `d:num` SUBST1_TAC) THEN
SPEC_TAC(`d:num`,`d:num`) THEN INDUCT_TAC THEN
REWRITE_TAC[ADD_CLAUSES; real_pow; REAL_LE_REFL] THEN
POP_ASSUM MP_TAC THEN MP_TAC(SPEC `m:num` REAL_LT_POW2) THEN
REAL_ARITH_TAC);;
let REAL_LE_SUC_POW2 = prove
(`!m. &2 pow m + &1 <= &2 pow (SUC m)`,
GEN_TAC THEN REWRITE_TAC[real_pow; REAL_MUL_2; REAL_LE_LADD; REAL_LE_POW2]);;
let REAL_OPPSIGN_LEMMA = prove
(`!x y. (x * y < &0) <=> (x < &0 /\ &0 < y) \/ (&0 < x /\ y < &0)`,
REPEAT GEN_TAC THEN
REPEAT_TCL DISJ_CASES_THEN ASSUME_TAC (SPEC `x:real` REAL_LT_NEGTOTAL) THEN
REPEAT_TCL DISJ_CASES_THEN ASSUME_TAC (SPEC `y:real` REAL_LT_NEGTOTAL) THEN
ASM_REWRITE_TAC[REAL_MUL_LZERO; REAL_MUL_RZERO; REAL_LT_REFL] THEN
POP_ASSUM_LIST(MP_TAC o end_itlist CONJ) THEN
DISCH_THEN(fun th -> MP_TAC(MATCH_MP REAL_LT_MUL th) THEN MP_TAC th) THEN
REWRITE_TAC[REAL_MUL_LNEG; REAL_MUL_RNEG; REAL_NEG_NEG] THEN
REAL_ARITH_TAC);;
let REAL_OPPSIGN = prove
(`(&0 < x ==> &0 <= y) /\ (x < &0 ==> y <= &0) <=> &0 <= x * y`,
REWRITE_TAC[GSYM REAL_NOT_LT; REAL_OPPSIGN_LEMMA] THEN
REAL_ARITH_TAC);;
let REAL_NDIV_LEMMA1a = prove
(`!a m n. &2 * abs(&2 pow m * &a - &2 pow (m + n)) <= &2 pow m
==> (&a = &2 pow n)`,
REPEAT GEN_TAC THEN REWRITE_TAC[REAL_POW_ADD; GSYM REAL_SUB_LDISTRIB] THEN
REWRITE_TAC[REAL_ABS_MUL; REAL_ABS_POW; REAL_ABS_NUM] THEN
REWRITE_TAC[REAL_OF_NUM_POW] THEN
REPEAT_TCL DISJ_CASES_THEN ASSUME_TAC
(SPECL [`a:num`; `2 EXP n`] LT_CASES) THEN
ASM_REWRITE_TAC[] THEN
CONV_TAC CONTRAPOS_CONV THEN DISCH_THEN(K ALL_TAC) THEN
POP_ASSUM(X_CHOOSE_THEN `d:num` SUBST1_TAC o REWRITE_RULE[LT_EXISTS]) THEN
REWRITE_TAC[GSYM REAL_OF_NUM_ADD] THEN
REWRITE_TAC[REAL_ARITH `((a + b) - a = b) /\ (a - (a + b) = --b)`] THEN
REWRITE_TAC[REAL_ABS_NEG; REAL_NOT_LE; REAL_ABS_NUM] THEN
REWRITE_TAC[ADD1; GSYM REAL_OF_NUM_ADD] THEN
REWRITE_TAC[REAL_MUL_2; REAL_ADD_LDISTRIB; REAL_ADD_RDISTRIB] THEN
REWRITE_TAC[REAL_MUL_RID; REAL_ADD_ASSOC; REAL_LT_ADDL] THEN
MATCH_MP_TAC REAL_LTE_TRANS THEN EXISTS_TAC `&(2 EXP m)` THEN
REWRITE_TAC[REAL_LT_POW2; GSYM REAL_OF_NUM_POW] THEN
ONCE_REWRITE_TAC[AC REAL_ADD_AC `(a + b) + c = b + (a + c)`] THEN
REWRITE_TAC[GSYM REAL_MUL_2; REAL_LE_ADDR] THEN
MATCH_MP_TAC REAL_LE_MUL THEN REWRITE_TAC[REAL_POS] THEN
MATCH_MP_TAC REAL_LE_MUL THEN REWRITE_TAC[REAL_POS] THEN
MATCH_MP_TAC REAL_LT_IMP_LE THEN REWRITE_TAC[REAL_LT_POW2]);;
let REAL_NDIV_LEMMA1b = prove
(`!a m n. ~(&2 * abs(-- (&2 pow m * &a) - &2 pow (m + n)) <= &2 pow m)`,
REPEAT GEN_TAC THEN REWRITE_TAC[real_sub; GSYM REAL_NEG_ADD] THEN
REWRITE_TAC[REAL_ABS_NEG; REAL_POW_ADD] THEN
REWRITE_TAC[REAL_ABS_MUL; GSYM REAL_ADD_LDISTRIB] THEN
SUBGOAL_THEN `&0 <= &a + &2 pow n` ASSUME_TAC THENL
[MATCH_MP_TAC REAL_LE_ADD THEN REWRITE_TAC[REAL_POS] THEN
MATCH_MP_TAC REAL_POW_LE THEN REWRITE_TAC[REAL_POS];
REWRITE_TAC[REAL_ABS_POW; REAL_ABS_NUM] THEN
ASM_REWRITE_TAC[real_abs; REAL_NOT_LE] THEN
MATCH_MP_TAC REAL_LTE_TRANS THEN
EXISTS_TAC `(&2 * &2 pow m) * &1` THEN CONJ_TAC THENL
[REWRITE_TAC[REAL_MUL_RID; REAL_MUL_2] THEN
REWRITE_TAC[REAL_LT_ADDR; REAL_LT_POW2];
REWRITE_TAC[REAL_MUL_ASSOC] THEN MATCH_MP_TAC REAL_LE_LMUL THEN
CONJ_TAC THENL
[MATCH_MP_TAC REAL_LE_MUL THEN REWRITE_TAC[REAL_POS] THEN
MATCH_MP_TAC REAL_POW_LE THEN REWRITE_TAC[REAL_POS];
MATCH_MP_TAC REAL_LE_TRANS THEN EXISTS_TAC `&2 pow n` THEN
REWRITE_TAC[REAL_LE_POW2; REAL_LE_ADDL; REAL_POS]]]]);;
let REAL_NDIV_LEMMA2 = prove
(`!a b m n. (?k. (b = &k) \/ (b = --(&k))) /\
(abs(a) = &2 pow m) /\
&2 * abs(a * b - &2 pow (m + n)) <= abs(a)
==> (a * b = &2 pow (m + n))`,
REPEAT GEN_TAC THEN
DISCH_THEN(CONJUNCTS_THEN2 STRIP_ASSUME_TAC MP_TAC) THEN
DISCH_THEN(CONJUNCTS_THEN2 ASSUME_TAC MP_TAC) THEN
DISJ_CASES_THEN SUBST1_TAC (REAL_ARITH `(a = abs a) \/ (a = --(abs a))`) THEN
ASM_REWRITE_TAC[REAL_MUL_LNEG; REAL_MUL_RNEG] THEN
REWRITE_TAC[REAL_ABS_NEG; REAL_ABS_POW; REAL_ABS_NUM; REAL_NEG_NEG] THEN
REWRITE_TAC[REAL_NDIV_LEMMA1b] THEN
DISCH_THEN(SUBST1_TAC o MATCH_MP REAL_NDIV_LEMMA1a) THEN
REWRITE_TAC[REAL_POW_ADD]);;
let REAL_NDIV_LEMMA3 = prove
(`!a b m n. m <= n /\
(?k. (b = &k) \/ (b = --(&k))) /\
(abs(a) = &2 pow m) /\
&2 * abs(a * b - &2 pow n) <= abs(a)
==> (a * b = &2 pow n)`,
REPEAT GEN_TAC THEN
DISCH_THEN(CONJUNCTS_THEN2 ASSUME_TAC MP_TAC) THEN
POP_ASSUM(CHOOSE_THEN SUBST1_TAC o REWRITE_RULE[LE_EXISTS]) THEN
REWRITE_TAC[REAL_NDIV_LEMMA2]);;
(* ------------------------------------------------------------------------- *)
(* Surely there is already an efficient way to do this... *)
(* ------------------------------------------------------------------------- *)
let log2 = (*** least p >= 0 with x <= 2^p ***)
let rec log2 x y =
if x </ Int 1 then y
else log2 (quo_num x (Int 2)) (y +/ Int 1) in
fun x -> log2 (x -/ Int 1) (Int 0);;
(* ------------------------------------------------------------------------- *)
(* Theorems justifying the steps. *)
(* ------------------------------------------------------------------------- *)
let REALCALC_DOWNGRADE = prove
(`(SUC d0 = d) ==>
(n + d = n0) ==>
abs(a - &2 pow n0 * x) < &1 ==>
abs((&2 pow d) * b - a) <= &2 pow d0 ==>
abs(b - &2 pow n * x) < &1`,
DISCH_THEN(SUBST1_TAC o SYM) THEN
DISCH_THEN(SUBST1_TAC o SYM) THEN
REPEAT DISCH_TAC THEN
MATCH_MP_TAC REAL_LT_LCANCEL_IMP THEN EXISTS_TAC `&2 pow (SUC d0)` THEN
CONJ_TAC THENL
[MATCH_MP_TAC REAL_POW_LT THEN REAL_ARITH_TAC;
REWRITE_TAC[REAL_ABS_LEMMA; REAL_MUL_RID; REAL_SUB_LDISTRIB] THEN
MATCH_MP_TAC REAL_LTE_TRANS THEN EXISTS_TAC `&2 pow d0 + &2 pow d0` THEN
CONJ_TAC THENL
[MATCH_MP_TAC REAL_ABS_TRIANGLE_LEMMA THEN EXISTS_TAC `a:real` THEN
MATCH_MP_TAC REAL_LTE_ADD2 THEN ASM_REWRITE_TAC[] THEN
MATCH_MP_TAC REAL_LTE_TRANS THEN EXISTS_TAC `&1` THEN
REWRITE_TAC[REAL_MUL_ASSOC; GSYM REAL_POW_ADD] THEN
ONCE_REWRITE_TAC[ADD_SYM] THEN ASM_REWRITE_TAC[] THEN
SPEC_TAC(`d0:num`,`d0:num`) THEN INDUCT_TAC THEN
REWRITE_TAC[real_pow; REAL_LE_REFL] THEN
MATCH_MP_TAC REAL_LE_TRANS THEN EXISTS_TAC `&1 + &1` THEN
REWRITE_TAC[REAL_MUL_2] THEN CONJ_TAC THENL
[REAL_ARITH_TAC;
MATCH_MP_TAC REAL_LE_ADD2 THEN ASM_REWRITE_TAC[]];
REWRITE_TAC[real_pow; GSYM REAL_MUL_2; REAL_LE_REFL]]]);;
let REALCALC_INT = prove
(`abs((&2 pow n) * a - (&2 pow n) * a) < &1`,
REWRITE_TAC[REAL_SUB_REFL; REAL_ABS_0; REAL_LT_01]);;
let REALCALC_NEG = prove
(`abs(a - (&2 pow n) * x) < &1
==> abs(--a - (&2 pow n) * --x) < &1`,
REWRITE_TAC[real_sub; GSYM REAL_NEG_ADD] THEN
REWRITE_TAC[REAL_ABS_NEG; REAL_MUL_RNEG]);;
let REALCALC_ABS = prove
(`abs(a - &2 pow n * x) < &1
==> abs(abs(a) - &2 pow n * abs(x)) < &1`,
DISCH_TAC THEN REWRITE_TAC[REAL_ABS_LEMMA] THEN
MATCH_MP_TAC REAL_LET_TRANS THEN
EXISTS_TAC `abs(a - (&2 pow n) * x)` THEN
ASM_REWRITE_TAC[REAL_ABS_SUB_ABS]);;
let REALCALC_INV_LEMMA = prove
(`(?m. (b = &m) \/ (b = --(&m))) /\
(?m. (a = &m) \/ (a = --(&m))) /\
SUC(n + k) <= (2 * e) /\
&2 pow e <= abs(a) /\
abs(a - &2 pow k * x) < &1 /\
&2 * abs(a * b - &2 pow (n + k)) <= abs(a)
==> abs(b - &2 pow n * inv(x)) < &1`,
let lemma1 = REAL_ARITH
`!x y z b. &2 * abs(x - y) <= b /\ &2 * abs(y - z) < b
==> &2 * abs(x - z) < &2 * b` in
let lemma2 = REAL_ARITH
`!x y z. x + &1 <= abs(z) /\ abs(z - y) < &1 ==> x <= abs(y)` in
let lemma3 = REAL_ARITH
`(abs(x) <= &1 /\ &0 < abs(y) /\ abs(y) < &1) /\
(&0 < x ==> &0 <= y) /\ (x < &0 ==> y <= &0)
==> abs(x - y) < &1` in
let lemma4 = REAL_ARITH
`!a b c. c <= abs(a) + abs(b) /\ abs(a - b) < c ==>
(&0 < a ==> &0 <= b) /\ (a < &0 ==> b <= &0)` in
DISCH_THEN(REPEAT_TCL CONJUNCTS_THEN ASSUME_TAC) THEN
SUBGOAL_THEN `~(a = &0)` ASSUME_TAC THENL
[DISCH_THEN SUBST_ALL_TAC THEN UNDISCH_TAC `&2 pow e <= abs(&0)` THEN
REWRITE_TAC[REAL_ABS_0; GSYM REAL_NOT_LT; REAL_LT_POW2]; ALL_TAC] THEN
SUBGOAL_THEN `~(x = &0)` ASSUME_TAC THENL
[DISCH_THEN SUBST_ALL_TAC THEN
UNDISCH_TAC `abs(a - &2 pow k * &0) < &1` THEN
REWRITE_TAC[REAL_MUL_RZERO; REAL_SUB_RZERO; REAL_NOT_LT] THEN
MATCH_MP_TAC REAL_LE_TRANS THEN EXISTS_TAC `&2 pow e` THEN
ASM_REWRITE_TAC[REAL_LE_POW2]; ALL_TAC] THEN
SUBGOAL_THEN `(&2 pow e + &1 <= abs(a)) \/ (&2 pow e = abs(a))` MP_TAC THENL
[REWRITE_TAC[REAL_OF_NUM_POW] THEN
FIRST_ASSUM(CHOOSE_THEN(DISJ_CASES_THEN SUBST_ALL_TAC)) THEN
REWRITE_TAC[REAL_ABS_NEG; REAL_ABS_NUM] THEN
RULE_ASSUM_TAC(REWRITE_RULE[REAL_ABS_NEG; REAL_ABS_NUM]) THEN
REWRITE_TAC[REAL_OF_NUM_ADD; REAL_OF_NUM_LE; REAL_OF_NUM_EQ] THEN
REWRITE_TAC[GSYM ADD1; LE_SUC_LT; GSYM LE_LT] THEN
ASM_REWRITE_TAC[GSYM REAL_OF_NUM_LE; GSYM REAL_OF_NUM_POW];
UNDISCH_TAC `&2 pow e <= abs(a)` THEN DISCH_THEN(K ALL_TAC)] THEN
DISCH_THEN(DISJ_CASES_THEN MP_TAC) THENL
[DISCH_TAC THEN MATCH_MP_TAC REAL_LT_LCANCEL_IMP THEN
EXISTS_TAC `&2 * abs(a)` THEN CONJ_TAC THENL
[MATCH_MP_TAC REAL_LT_MUL THEN
ASM_REWRITE_TAC[GSYM REAL_ABS_NZ] THEN REAL_ARITH_TAC;
REWRITE_TAC[GSYM REAL_MUL_ASSOC; GSYM REAL_ABS_MUL] THEN
REWRITE_TAC[REAL_SUB_LDISTRIB; REAL_MUL_RID] THEN
MATCH_MP_TAC lemma1 THEN EXISTS_TAC `&2 pow (n + k)` THEN
ASM_REWRITE_TAC[]] THEN
GEN_REWRITE_TAC (LAND_CONV o funpow 3 RAND_CONV) [REAL_MUL_SYM] THEN
REWRITE_TAC[REAL_POW_ADD; GSYM REAL_MUL_ASSOC] THEN
REWRITE_TAC[GSYM REAL_SUB_LDISTRIB; REAL_ABS_MUL] THEN
MATCH_MP_TAC REAL_LT_RCANCEL_IMP THEN
EXISTS_TAC `abs(x)` THEN ASM_REWRITE_TAC[GSYM REAL_ABS_NZ] THEN
REWRITE_TAC[GSYM REAL_MUL_ASSOC] THEN
ONCE_REWRITE_TAC[GSYM REAL_ABS_MUL] THEN
MATCH_MP_TAC REAL_LTE_TRANS THEN
EXISTS_TAC `&2 * abs(&2 pow n) * &1` THEN CONJ_TAC THENL
[MATCH_MP_TAC REAL_LT_LMUL THEN
CONJ_TAC THENL [REAL_ARITH_TAC; ALL_TAC] THEN
MATCH_MP_TAC REAL_LT_LMUL THEN CONJ_TAC THENL
[REWRITE_TAC[GSYM REAL_ABS_NZ; REAL_POW_EQ_0] THEN
CONV_TAC(RAND_CONV(LAND_CONV REAL_INT_EQ_CONV)) THEN REWRITE_TAC[];
REWRITE_TAC[REAL_SUB_RDISTRIB] THEN
ONCE_REWRITE_TAC[REAL_ABS_SUB] THEN
GEN_REWRITE_TAC (LAND_CONV o RAND_CONV o LAND_CONV) [REAL_MUL_SYM] THEN
REWRITE_TAC[REAL_MUL_ASSOC] THEN
FIRST_ASSUM(fun th -> REWRITE_TAC[MATCH_MP REAL_MUL_RINV th]) THEN
ASM_REWRITE_TAC[REAL_MUL_LID]];
ALL_TAC] THEN
MATCH_MP_TAC REAL_LE_LCANCEL_IMP THEN EXISTS_TAC `&2 pow k` THEN
REWRITE_TAC[REAL_LT_POW2; REAL_MUL_RID; REAL_ABS_LEMMA] THEN
ONCE_REWRITE_TAC
[AC REAL_MUL_AC `a * b * c = (a * c) * b`] THEN
REWRITE_TAC[REAL_ABS_MUL; REAL_ABS_POW; REAL_ABS_NUM] THEN
MATCH_MP_TAC REAL_LE_TRANS THEN
EXISTS_TAC `&2 pow e * &2 pow e` THEN CONJ_TAC THENL
[ONCE_REWRITE_TAC
[AC REAL_MUL_AC `(a * b) * c = c * b * a`] THEN
REWRITE_TAC[GSYM REAL_POW_ADD; GSYM(CONJUNCT2 real_pow)] THEN
MATCH_MP_TAC REAL_MONO_POW2 THEN ASM_REWRITE_TAC[GSYM MULT_2];
MATCH_MP_TAC REAL_LE_MUL2 THEN REPEAT CONJ_TAC THENL
[MATCH_MP_TAC REAL_LT_IMP_LE THEN REWRITE_TAC[REAL_LT_POW2];
REWRITE_TAC[REAL_ABS_LEMMA] THEN MATCH_MP_TAC lemma2 THEN
EXISTS_TAC `a:real` THEN ASM_REWRITE_TAC[];
MATCH_MP_TAC REAL_LT_IMP_LE THEN REWRITE_TAC[REAL_LT_POW2];
MATCH_MP_TAC REAL_LE_TRANS THEN EXISTS_TAC `&2 pow e + &1` THEN
ASM_REWRITE_TAC[] THEN REAL_ARITH_TAC]];
DISCH_TAC THEN
DISJ_CASES_TAC (SPECL [`e:num`; `n + k:num`] LET_CASES) THENL
[SUBGOAL_THEN `a * b = &2 pow (n + k)` ASSUME_TAC THENL
[MATCH_MP_TAC REAL_NDIV_LEMMA3 THEN
EXISTS_TAC `e:num` THEN ASM_REWRITE_TAC[]; ALL_TAC] THEN
MATCH_MP_TAC REAL_LT_LCANCEL_IMP THEN EXISTS_TAC `abs(a)` THEN
ASM_REWRITE_TAC[GSYM REAL_ABS_NZ; GSYM REAL_ABS_MUL] THEN
ASM_REWRITE_TAC[REAL_SUB_LDISTRIB] THEN
ONCE_REWRITE_TAC[AC REAL_MUL_AC `a * b * c = b * a * c`] THEN
REWRITE_TAC[REAL_POW_ADD; GSYM REAL_SUB_LDISTRIB] THEN
REWRITE_TAC[REAL_ABS_MUL; REAL_MUL_RID] THEN
MATCH_MP_TAC REAL_LT_RCANCEL_IMP THEN EXISTS_TAC `abs(x)` THEN
ASM_REWRITE_TAC[GSYM REAL_ABS_NZ; GSYM REAL_MUL_ASSOC] THEN
GEN_REWRITE_TAC (LAND_CONV o RAND_CONV) [GSYM REAL_ABS_MUL] THEN
REWRITE_TAC[REAL_SUB_RDISTRIB; GSYM REAL_MUL_ASSOC] THEN
REWRITE_TAC[MATCH_MP REAL_MUL_LINV (ASSUME `~(x = &0)`)] THEN
ONCE_REWRITE_TAC[REAL_ABS_SUB] THEN
MATCH_MP_TAC REAL_LTE_TRANS THEN EXISTS_TAC `&2 pow n * &1` THEN
CONJ_TAC THENL
[REWRITE_TAC[REAL_ABS_POW; REAL_ABS_NUM] THEN
MATCH_MP_TAC REAL_LT_LMUL THEN
ASM_REWRITE_TAC[REAL_LT_POW2; REAL_MUL_RID];
MATCH_MP_TAC REAL_LE_RCANCEL_IMP THEN EXISTS_TAC `&2 pow (SUC k)` THEN
REWRITE_TAC[REAL_MUL_RID; REAL_LT_POW2]] THEN
MATCH_MP_TAC REAL_LE_TRANS THEN
EXISTS_TAC `&2 pow (2 * e)` THEN CONJ_TAC THENL
[REWRITE_TAC[GSYM REAL_POW_ADD; ADD_CLAUSES] THEN
MATCH_MP_TAC REAL_MONO_POW2 THEN ASM_REWRITE_TAC[];
SUBST1_TAC(SYM(ASSUME `&2 pow e = abs(a)`)) THEN
REWRITE_TAC[MULT_2; REAL_POW_ADD; GSYM REAL_MUL_ASSOC] THEN
MATCH_MP_TAC REAL_LE_LMUL THEN
REWRITE_TAC[MATCH_MP REAL_LT_IMP_LE (SPEC_ALL REAL_LT_POW2)]] THEN
ONCE_REWRITE_TAC[REAL_MUL_SYM] THEN REWRITE_TAC[real_pow] THEN
SUBGOAL_THEN `?d. e = SUC d` (CHOOSE_THEN SUBST_ALL_TAC) THENL
[UNDISCH_TAC `SUC (n + k) <= (2 * e)` THEN
SPEC_TAC(`e:num`,`e:num`) THEN INDUCT_TAC THEN
REWRITE_TAC[MULT_CLAUSES; ADD_CLAUSES; LE; NOT_SUC] THEN
REWRITE_TAC[SUC_INJ; GSYM EXISTS_REFL];
REWRITE_TAC[real_pow; GSYM REAL_MUL_ASSOC] THEN
MATCH_MP_TAC REAL_LE_LMUL THEN REWRITE_TAC[REAL_POS] THEN
MATCH_MP_TAC REAL_LE_TRANS THEN
EXISTS_TAC `&2 pow (SUC d) - &1` THEN
REWRITE_TAC[REAL_LE_SUB_RADD; REAL_LE_SUB_LADD] THEN
REWRITE_TAC[REAL_LE_SUC_POW2] THEN
SUBGOAL_THEN `abs(abs a - &2 pow k * abs(x)) < &1` MP_TAC THENL
[REWRITE_TAC[REAL_ABS_LEMMA] THEN
MATCH_MP_TAC(REAL_LET_IMP REAL_ABS_SUB_ABS) THEN
ASM_REWRITE_TAC[];
ASM_REWRITE_TAC[] THEN REAL_ARITH_TAC]];
SUBGOAL_THEN `abs(b) <= &1 /\ &0 <= a * b` STRIP_ASSUME_TAC THENL
[ASM_CASES_TAC `b = &0` THEN
ASM_REWRITE_TAC[REAL_ABS_0; REAL_MUL_RZERO; REAL_POS] THEN
SUBGOAL_THEN `abs(a) <= abs(a * b)` ASSUME_TAC THENL
[GEN_REWRITE_TAC (LAND_CONV o RAND_CONV) [GSYM REAL_MUL_RID] THEN
REWRITE_TAC[REAL_ABS_MUL] THEN MATCH_MP_TAC REAL_LE_LMUL THEN
REWRITE_TAC[REAL_ABS_POS] THEN
SUBGOAL_THEN `?q. abs(b) = &q` CHOOSE_TAC THENL
[UNDISCH_TAC `?m. (b = &m) \/ (b = --(&m))` THEN
DISCH_THEN(X_CHOOSE_THEN `p:num` DISJ_CASES_TAC) THEN
EXISTS_TAC `p:num` THEN
ASM_REWRITE_TAC[REAL_ABS_NEG; REAL_ABS_NUM];
UNDISCH_TAC `~(b = &0)` THEN ASM_REWRITE_TAC[REAL_ABS_NZ] THEN
REWRITE_TAC[REAL_ABS_NUM; REAL_OF_NUM_LE; REAL_OF_NUM_LT] THEN
REWRITE_TAC[SYM(REWRITE_CONV[ARITH_SUC] `SUC 0`)] THEN
REWRITE_TAC[LE_SUC_LT]];
ALL_TAC] THEN
SUBGOAL_THEN `abs(a * b) <= abs(a) /\ &0 <= a * b` ASSUME_TAC THENL
[MP_TAC(SPEC `(n:num) + k` REAL_LT_POW2) THEN
UNDISCH_TAC `&2 * abs(a * b - &2 pow (n + k)) <= abs a` THEN
UNDISCH_TAC `abs(a) <= abs(a * b)` THEN
SUBGOAL_THEN `~(a * b = &0)` MP_TAC THENL
[ASM_REWRITE_TAC[REAL_ENTIRE]; ALL_TAC] THEN
SUBGOAL_THEN `&2 * &2 pow (n + k) <= abs(a)` MP_TAC THENL
[REWRITE_TAC[GSYM(CONJUNCT2 real_pow)] THEN
FIRST_ASSUM(fun th -> GEN_REWRITE_TAC RAND_CONV [SYM th]) THEN
MATCH_MP_TAC REAL_MONO_POW2 THEN ASM_REWRITE_TAC[LE_SUC_LT];
REAL_ARITH_TAC];
ASM_REWRITE_TAC[] THEN MATCH_MP_TAC REAL_LE_LCANCEL_IMP THEN
EXISTS_TAC `abs(a)` THEN ASM_REWRITE_TAC
[GSYM REAL_ABS_NZ; GSYM REAL_ABS_MUL; REAL_MUL_RID]];
ALL_TAC] THEN
MATCH_MP_TAC lemma3 THEN CONJ_TAC THENL
[ASM_REWRITE_TAC[] THEN CONJ_TAC THENL
[ASM_REWRITE_TAC[GSYM REAL_ABS_NZ; REAL_ENTIRE; REAL_INV_EQ_0] THEN
MATCH_MP_TAC REAL_LT_IMP_NZ THEN REWRITE_TAC[REAL_LT_POW2];
MATCH_MP_TAC REAL_LT_LCANCEL_IMP THEN EXISTS_TAC `abs(x)` THEN
ASM_REWRITE_TAC[GSYM REAL_ABS_NZ; GSYM REAL_ABS_MUL] THEN
ONCE_REWRITE_TAC[AC REAL_MUL_AC `a * b * c = b * c * a`] THEN
SUBGOAL_THEN `inv(x) * x = &1` SUBST1_TAC THENL
[MATCH_MP_TAC REAL_MUL_LINV THEN ASM_REWRITE_TAC[];
REWRITE_TAC[REAL_MUL_RID] THEN
MATCH_MP_TAC REAL_LT_LCANCEL_IMP THEN EXISTS_TAC `&2 pow k` THEN
REWRITE_TAC[REAL_LT_POW2; REAL_ABS_LEMMA] THEN
MATCH_MP_TAC REAL_LET_TRANS THEN
EXISTS_TAC `&2 pow (SUC(n + k)) - &1` THEN
REWRITE_TAC[REAL_LT_SUB_RADD; REAL_LE_SUB_LADD] THEN
ONCE_REWRITE_TAC[ADD_SYM] THEN
REWRITE_TAC[GSYM REAL_POW_ADD] THEN
ONCE_REWRITE_TAC[ADD_SYM] THEN
REWRITE_TAC[REAL_LE_SUC_POW2; REAL_ABS_POW; REAL_ABS_NUM] THEN
MATCH_MP_TAC REAL_LET_TRANS THEN EXISTS_TAC `&2 pow e` THEN
CONJ_TAC THENL
[MATCH_MP_TAC REAL_MONO_POW2 THEN
ASM_REWRITE_TAC[LE_SUC_LT];
UNDISCH_TAC `abs(a - &2 pow k * x) < &1` THEN
ASM_REWRITE_TAC[] THEN REAL_ARITH_TAC]]];
SUBGOAL_THEN `&0 <= b * (&2 pow n * inv x)` MP_TAC THENL
[MATCH_MP_TAC REAL_LE_LCANCEL_IMP THEN
EXISTS_TAC `a * a` THEN ASM_REWRITE_TAC[REAL_LT_SQUARE] THEN
REWRITE_TAC[REAL_MUL_RZERO] THEN
ONCE_REWRITE_TAC[AC REAL_MUL_AC
`(a * b) * c * d = (a * c) * (b * d)`] THEN
MATCH_MP_TAC REAL_LE_MUL THEN ASM_REWRITE_TAC[] THEN
MATCH_MP_TAC REAL_LE_LCANCEL_IMP THEN
EXISTS_TAC `x * x` THEN ASM_REWRITE_TAC[REAL_LT_SQUARE] THEN
REWRITE_TAC[REAL_MUL_RZERO] THEN
ONCE_REWRITE_TAC[AC REAL_MUL_AC
`(a * b) * c * d * e = d * (e * a) * c * b`] THEN
MATCH_MP_TAC REAL_LE_MUL THEN
REWRITE_TAC[MATCH_MP REAL_LT_IMP_LE (SPEC_ALL REAL_LT_POW2)] THEN
FIRST_ASSUM(fun th -> GEN_REWRITE_TAC (RAND_CONV o LAND_CONV)
[MATCH_MP REAL_MUL_LINV th]) THEN
MATCH_MP_TAC REAL_LE_LCANCEL_IMP THEN EXISTS_TAC `&2 pow k` THEN
REWRITE_TAC[REAL_LT_POW2; REAL_MUL_RZERO; REAL_MUL_LID] THEN
ONCE_REWRITE_TAC[AC REAL_MUL_AC `a * b * c = b * (a * c)`] THEN
ONCE_REWRITE_TAC[GSYM REAL_OPPSIGN] THEN
MATCH_MP_TAC lemma4 THEN EXISTS_TAC `&1` THEN
ASM_REWRITE_TAC[] THEN MATCH_MP_TAC REAL_LE_TRANS THEN
EXISTS_TAC `abs(a)` THEN CONJ_TAC THENL
[UNDISCH_TAC `?m. (a = &m) \/ (a = -- (&m))` THEN
DISCH_THEN(CHOOSE_THEN(DISJ_CASES_THEN SUBST_ALL_TAC)) THEN
ASM_REWRITE_TAC[REAL_ABS_NEG; REAL_ABS_NUM] THEN
REWRITE_TAC[REAL_OF_NUM_LE] THEN
REWRITE_TAC[SYM(REWRITE_CONV[ARITH_SUC] `SUC 0`)] THEN
REWRITE_TAC[LE_SUC_LT] THEN RULE_ASSUM_TAC
(REWRITE_RULE[REAL_ARITH `(--x = &0) = (x = &0)`]) THEN
UNDISCH_TAC `~(&m = &0)` THEN REWRITE_TAC[REAL_OF_NUM_EQ] THEN
CONV_TAC CONTRAPOS_CONV THEN REWRITE_TAC[NOT_LT; LE];
REWRITE_TAC[REAL_LE_ADDR; REAL_ABS_POS]];
REWRITE_TAC[REAL_OPPSIGN]]]]]);;
let REALCALC_INV = prove
(`abs(a - &2 pow k * x) < &1 ==>
(?m. (a = &m) \/ (a = --(&m))) ==>
(?m. (b = &m) \/ (b = --(&m))) ==>
SUC(n + k) <= (2 * e) ==>
&2 pow e <= abs(a) ==>
&2 * abs(a * b - &2 pow (n + k)) <= abs(a)
==> abs(b - &2 pow n * inv(x)) < &1`,
REPEAT DISCH_TAC THEN MATCH_MP_TAC REALCALC_INV_LEMMA THEN
ASM_REWRITE_TAC[]);;
let REALCALC_ADD = prove
(`(n + 2 = n') ==>
abs(a - &2 pow n' * x) < &1 ==>
abs(b - &2 pow n' * y) < &1 ==>
abs(&4 * c - (a + b)) <= &2
==> abs(c - &2 pow n * (x + y)) < &1`,
DISCH_THEN(SUBST_ALL_TAC o SYM) THEN REPEAT DISCH_TAC THEN
MATCH_MP_TAC REAL_LT_LCANCEL_IMP THEN
EXISTS_TAC `&2 pow 2` THEN
CONV_TAC(LAND_CONV REAL_INT_REDUCE_CONV) THEN
REWRITE_TAC[REAL_ABS_LEMMA; REAL_SUB_LDISTRIB; REAL_MUL_RID] THEN
REWRITE_TAC[REAL_MUL_ASSOC; GSYM REAL_POW_ADD] THEN
ONCE_REWRITE_TAC[ADD_SYM] THEN
SUBST1_TAC(REAL_INT_REDUCE_CONV `&2 pow 2`) THEN
MATCH_MP_TAC REAL_ABS_TRIANGLE_LEMMA THEN
EXISTS_TAC `a + b` THEN
GEN_REWRITE_TAC RAND_CONV [SYM(REAL_INT_REDUCE_CONV `&2 + &2`)] THEN
MATCH_MP_TAC REAL_LTE_ADD2 THEN ASM_REWRITE_TAC[] THEN ONCE_REWRITE_TAC
[REAL_ARITH `(x + y) - a * (u + v) = (x - a * u) + (y - a * v)`] THEN
GEN_REWRITE_TAC RAND_CONV [SYM(REAL_INT_REDUCE_CONV `&1 + &1`)] THEN
MATCH_MP_TAC(REAL_LET_IMP REAL_ABS_TRIANGLE) THEN
MATCH_MP_TAC REAL_LT_ADD2 THEN ASM_REWRITE_TAC[]);;
let REALCALC_MUL = prove
(`abs(a - &2 pow k * x) < &1 ==>
abs(b - &2 pow l * y) < &1 ==>
(n + m = k + l) ==>
&2 * (abs(a) + abs(b) + &1) <= &2 pow m ==>
&2 * abs(&2 pow m * c - a * b) <= &2 pow m
==> abs(c - &2 pow n * (x * y)) < &1`,
REPEAT STRIP_TAC THEN
MATCH_MP_TAC REAL_LT_LCANCEL_IMP THEN EXISTS_TAC `&2 pow m` THEN
REWRITE_TAC[REAL_LT_POW2; REAL_ABS_LEMMA; REAL_SUB_LDISTRIB] THEN
MATCH_MP_TAC REAL_LT_LCANCEL_IMP THEN EXISTS_TAC `&2` THEN
CONV_TAC(LAND_CONV (EQT_INTRO o REAL_ARITH)) THEN
REWRITE_TAC[REAL_MUL_RID] THEN
GEN_REWRITE_TAC RAND_CONV [REAL_MUL_2] THEN
MATCH_MP_TAC REAL_LET_TRANS THEN
EXISTS_TAC `&2 * abs(&2 pow m * c - a * b) +
&2 * abs(a * b - &2 pow m * &2 pow n * x * y)` THEN
CONV_TAC(LAND_CONV (EQT_INTRO o REAL_ARITH)) THEN REWRITE_TAC[] THEN
MATCH_MP_TAC REAL_LET_ADD2 THEN ASM_REWRITE_TAC[] THEN
REWRITE_TAC[REAL_MUL_ASSOC; GSYM REAL_POW_ADD] THEN
ONCE_REWRITE_TAC[ADD_SYM] THEN ASM_REWRITE_TAC[] THEN
REWRITE_TAC[REAL_POW_ADD] THEN
ONCE_REWRITE_TAC[AC REAL_MUL_AC `((a * b) * c) * d = (a * c) * (b * d)`] THEN
SUBGOAL_THEN `?d. abs(d) < &1 /\ (&2 pow k * x = a + d)` MP_TAC THENL
[EXISTS_TAC `&2 pow k * x - a` THEN
UNDISCH_TAC `abs(a - &2 pow k * x) < &1` THEN REAL_ARITH_TAC;
DISCH_THEN(CHOOSE_THEN(CONJUNCTS_THEN2 ASSUME_TAC SUBST1_TAC))] THEN
SUBGOAL_THEN `?e. abs(e) < &1 /\ (&2 pow l * y = b + e)` MP_TAC THENL
[EXISTS_TAC `&2 pow l * y - b` THEN
UNDISCH_TAC `abs(b - &2 pow l * y) < &1` THEN REAL_ARITH_TAC;
DISCH_THEN(CHOOSE_THEN(CONJUNCTS_THEN2 ASSUME_TAC SUBST1_TAC))] THEN
MATCH_MP_TAC REAL_LTE_TRANS THEN
EXISTS_TAC `&2 * (abs(a) * &1 + abs(b) * &1 + &1 * &1)` THEN CONJ_TAC THENL
[MATCH_MP_TAC REAL_LT_LMUL THEN
CONV_TAC(LAND_CONV (EQT_INTRO o REAL_ARITH)) THEN REWRITE_TAC[] THEN
MATCH_MP_TAC REAL_LET_TRANS THEN
EXISTS_TAC `abs(a) * abs(e) + abs(b) * abs(d) + abs(d) * abs(e)` THEN
CONJ_TAC THENL
[REWRITE_TAC[GSYM REAL_ABS_MUL] THEN REAL_ARITH_TAC;
MATCH_MP_TAC REAL_LET_ADD2 THEN CONJ_TAC THENL
[MATCH_MP_TAC REAL_LE_LMUL THEN REWRITE_TAC[REAL_ABS_POS] THEN
MATCH_MP_TAC REAL_LT_IMP_LE THEN ASM_REWRITE_TAC[];
MATCH_MP_TAC REAL_LET_ADD2 THEN CONJ_TAC THENL
[MATCH_MP_TAC REAL_LE_LMUL THEN REWRITE_TAC[REAL_ABS_POS] THEN
MATCH_MP_TAC REAL_LT_IMP_LE THEN ASM_REWRITE_TAC[];
MATCH_MP_TAC REAL_LT_MUL2 THEN ASM_REWRITE_TAC[REAL_ABS_POS]]]];
ASM_REWRITE_TAC[REAL_MUL_RID]]);;
(* ------------------------------------------------------------------------- *)
(* Square root. *)
(* ------------------------------------------------------------------------- *)
let REALCALC_SQRT = prove
(`abs(a - &2 pow n * x) < &1
==> &1 <= x
==> abs(b pow 2 - &2 pow n * a) <= b
==> abs(b - &2 pow n * sqrt(x)) < &1`,
REPEAT STRIP_TAC THEN
MATCH_MP_TAC REAL_LT_LCANCEL_IMP THEN
EXISTS_TAC `abs(b + &2 pow n * sqrt(x))` THEN CONJ_TAC THENL
[MATCH_MP_TAC(REAL_ARITH
`!z. abs(z) <= b /\ &0 < c ==> &0 < abs(b + c)`) THEN
EXISTS_TAC `b pow 2 - &2 pow n * a` THEN ASM_REWRITE_TAC[] THEN
ASM_SIMP_TAC[REAL_POW_LT; REAL_OF_NUM_LT; ARITH; REAL_LT_MUL;
SQRT_POS_LT; REAL_ARITH `&1 <= x ==> &0 < x`]; ALL_TAC] THEN
REWRITE_TAC[GSYM REAL_ABS_MUL; REAL_MUL_RID] THEN
ONCE_REWRITE_TAC[REAL_ARITH
`(a + b) * (a - b) = a * a - b * b`] THEN
MATCH_MP_TAC(REAL_ARITH
`!c d. abs(b - c) <= d /\ abs(c - a) < e - d
==> abs(b - a) < e`) THEN
MAP_EVERY EXISTS_TAC [`&2 pow n * a`; `b:real`] THEN
ASM_REWRITE_TAC[GSYM REAL_POW_2] THEN
REWRITE_TAC[REAL_POW_2; GSYM REAL_MUL_ASSOC] THEN
REWRITE_TAC[GSYM REAL_SUB_LDISTRIB; REAL_ABS_MUL] THEN
MATCH_MP_TAC(REAL_ARITH `a < c ==> a < abs(b + c) - b`) THEN
REWRITE_TAC[REAL_ABS_POW; REAL_ABS_NUM] THEN
MATCH_MP_TAC REAL_LT_LMUL THEN
SIMP_TAC[REAL_POW_LT; REAL_OF_NUM_LT; ARITH] THEN
ONCE_REWRITE_TAC[REAL_MUL_SYM] THEN
MATCH_MP_TAC REAL_LTE_TRANS THEN EXISTS_TAC `&1` THEN
ASM_SIMP_TAC[GSYM REAL_MUL_ASSOC; GSYM POW_2; SQRT_POW_2;
REAL_ARITH `&1 <= x ==> &0 <= x`] THEN
FIRST_ASSUM(ASSUME_TAC o MATCH_MP(REAL_ARITH `&1 <= x ==> &0 <= x`)) THEN
UNDISCH_TAC `&1 <= x` THEN CONV_TAC CONTRAPOS_CONV THEN
REWRITE_TAC[REAL_NOT_LE] THEN DISCH_TAC THEN
SUBGOAL_THEN `x = sqrt(x) pow 2` SUBST1_TAC THENL
[CONV_TAC SYM_CONV THEN ASM_REWRITE_TAC[SQRT_POW2];
GEN_REWRITE_TAC RAND_CONV [GSYM REAL_MUL_LID] THEN
REWRITE_TAC[POW_2] THEN MATCH_MP_TAC REAL_LT_MUL2 THEN
ASM_SIMP_TAC[SQRT_POS_LE]]);;
(* ------------------------------------------------------------------------- *)
(* Lemmas common to all the Taylor series error analyses. *)
(* ------------------------------------------------------------------------- *)
let STEP_LEMMA1 = prove
(`!a b c d x y.
abs(a - c) <= x /\ abs(b - d) <= y
==> abs(a * b - c * d) <= abs(c) * y + abs(d) * x + x * y`,
REPEAT GEN_TAC THEN
ABBREV_TAC `u = a - c` THEN ABBREV_TAC `v = b - d` THEN
SUBGOAL_THEN `a = c + u` SUBST1_TAC THENL
[POP_ASSUM_LIST(MP_TAC o end_itlist CONJ) THEN REAL_ARITH_TAC; ALL_TAC] THEN
SUBGOAL_THEN `b = d + v` SUBST1_TAC THENL
[POP_ASSUM_LIST(MP_TAC o end_itlist CONJ) THEN REAL_ARITH_TAC; ALL_TAC] THEN
STRIP_TAC THEN SUBST1_TAC
(REAL_ARITH `(c + u) * (d + v) - c * d = c * v + d * u + u * v`) THEN
REPEAT(MATCH_MP_TAC (REAL_LE_IMP REAL_ABS_TRIANGLE) THEN
MATCH_MP_TAC REAL_LE_ADD2 THEN CONJ_TAC) THEN
REWRITE_TAC[REAL_ABS_MUL] THENL
[MATCH_MP_TAC REAL_LE_LMUL;
MATCH_MP_TAC REAL_LE_LMUL;
MATCH_MP_TAC REAL_LE_MUL2] THEN
ASM_REWRITE_TAC[REAL_ABS_POS]);;
let STEP_LEMMA2 = prove
(`!n s t u x y k l a d.
&0 < a /\
&0 < d /\
abs(s - &2 pow n * x) <= k /\
abs(t - &2 pow n * y) <= l /\
&2 * abs(u * &2 pow n * d - a * s * t) <= &2 pow n * d
==> abs(u - &2 pow n * (a / d) * (x * y)) <=
(a / d) * (abs(x) + k / (&2 pow n)) * l +
((a / d) * k * abs(y) + &1 / &2)`,
REPEAT GEN_TAC THEN DISCH_THEN(CONJUNCTS_THEN2 ASSUME_TAC MP_TAC) THEN
DISCH_THEN(CONJUNCTS_THEN2 ASSUME_TAC MP_TAC) THEN
ONCE_REWRITE_TAC[CONJ_ASSOC] THEN DISCH_THEN
(CONJUNCTS_THEN2 (ASSUME_TAC o MATCH_MP STEP_LEMMA1) ASSUME_TAC) THEN
SUBGOAL_THEN `&0 < &2 * &2 pow n * d` ASSUME_TAC THENL
[REPEAT(MATCH_MP_TAC REAL_LT_MUL THEN CONJ_TAC) THEN
ASM_REWRITE_TAC[REAL_LT_POW2] THEN REAL_ARITH_TAC; ALL_TAC] THEN
MATCH_MP_TAC REAL_LE_LCANCEL_IMP THEN
EXISTS_TAC `&2 * &2 pow n * d` THEN ASM_REWRITE_TAC[] THEN
REWRITE_TAC[real_div; REAL_ADD_LDISTRIB; REAL_ADD_RDISTRIB] THEN
SUBGOAL_THEN
`!z. (&2 * &2 pow n * d) * abs(z) = abs((&2 * &2 pow n * d) * z)`
(fun th -> REWRITE_TAC[th])
THENL
[GEN_TAC THEN ONCE_REWRITE_TAC[REAL_ABS_MUL] THEN AP_THM_TAC THEN
AP_TERM_TAC THEN UNDISCH_TAC `&0 < &2 * &2 pow n * d` THEN
REAL_ARITH_TAC; ALL_TAC] THEN
REWRITE_TAC[REAL_SUB_LDISTRIB] THEN
(MATCH_MP_TAC o GEN_ALL o REAL_ARITH)
`abs(a - b) + abs(b - c) <= d ==> abs(a - c) <= d` THEN
EXISTS_TAC `&2 * a * s * t` THEN
REWRITE_TAC[GSYM REAL_MUL_ASSOC; REAL_ADD_ASSOC] THEN
GEN_REWRITE_TAC RAND_CONV [REAL_ADD_SYM] THEN
SUBGOAL_THEN `(inv(&2) * &2 = &1) /\
(inv(&2 pow n) * &2 pow n = &1) /\
(inv(d) * d = &1)`
STRIP_ASSUME_TAC THENL
[REPEAT CONJ_TAC THEN MATCH_MP_TAC REAL_MUL_LINV THEN
REWRITE_TAC[REAL_POW_EQ_0] THEN
UNDISCH_TAC `&0 < d` THEN REAL_ARITH_TAC; ALL_TAC] THEN
MATCH_MP_TAC REAL_LE_ADD2 THEN CONJ_TAC THENL
[GEN_REWRITE_TAC RAND_CONV [REAL_MUL_SYM] THEN
ASM_REWRITE_TAC[GSYM REAL_MUL_ASSOC; REAL_MUL_RID] THEN
REWRITE_TAC[GSYM REAL_SUB_LDISTRIB; GSYM REAL_ABS_LEMMA1] THEN
REWRITE_TAC[REAL_MUL_ASSOC] THEN
GEN_REWRITE_TAC (LAND_CONV o funpow 2 RAND_CONV o LAND_CONV)
[REAL_MUL_SYM] THEN ASM_REWRITE_TAC[GSYM REAL_MUL_ASSOC];
REWRITE_TAC(map (GSYM o SPEC `&2`)
[REAL_SUB_LDISTRIB; REAL_ADD_LDISTRIB]) THEN
REWRITE_TAC[GSYM REAL_ABS_LEMMA1] THEN MATCH_MP_TAC REAL_LE_LMUL THEN
CONV_TAC(LAND_CONV (EQT_INTRO o REAL_ARITH)) THEN REWRITE_TAC[] THEN
GEN_REWRITE_TAC (LAND_CONV o ONCE_DEPTH_CONV)
[AC REAL_MUL_AC
`a * b * c * d * e * f * g = d * (a * f) * (c * g) * (e * b)`] THEN
GEN_REWRITE_TAC (RAND_CONV o LAND_CONV o LAND_CONV)
[AC REAL_MUL_AC
`a * b * c * d * e * f = c * (a * e) * f * (d * b)`] THEN
GEN_REWRITE_TAC (RAND_CONV o LAND_CONV o RAND_CONV)
[AC REAL_MUL_AC
`a * b * c * d * e * f * g = c * (e * g) * (f * a) * (d * b)`] THEN
GEN_REWRITE_TAC (RAND_CONV o RAND_CONV)
[AC REAL_MUL_AC
`a * b * c * d * e * f = c * (a * f) * e * (d * b)`] THEN
GEN_REWRITE_TAC RAND_CONV
[AC REAL_ADD_AC `(a + b) + c = a + c + b`] THEN
ASM_REWRITE_TAC[REAL_MUL_RID] THEN
REWRITE_TAC[GSYM REAL_ADD_LDISTRIB; GSYM REAL_SUB_LDISTRIB] THEN
REWRITE_TAC[REAL_ABS_MUL] THEN
SUBGOAL_THEN `abs(a) = a` SUBST1_TAC THENL
[UNDISCH_TAC `&0 < a` THEN REAL_ARITH_TAC;
MATCH_MP_TAC REAL_LE_LMUL THEN ASM_REWRITE_TAC[REAL_ABS_LEMMA] THEN
MATCH_MP_TAC REAL_LT_IMP_LE THEN ASM_REWRITE_TAC[]]]);;
(* ------------------------------------------------------------------------- *)
(* Now specific instances. *)
(* ------------------------------------------------------------------------- *)
let STEP_EXP = prove
(`abs(x) <= &1 /\
abs(s - &2 pow n * x) <= &1 /\
abs(t - &2 pow n * (x pow i / &(FACT i))) <= k /\
&2 * abs(u * &2 pow n * &(SUC i) - s * t) <= &2 pow n * &(SUC i)
==> abs(u - &2 pow n * (x pow (SUC i)) / &(FACT(SUC i))) <=
(&2 / &(SUC i)) * k + &1 / &(FACT(SUC i)) + &1 / &2`,
STRIP_TAC THEN
MP_TAC(SPECL [`n:num`; `s:real`; `t:real`; `u:real`;
`x:real`; `x pow i / &(FACT i)`;
`&1`; `k:real`; `&1`; `&(SUC i)`] STEP_LEMMA2) THEN
ASM_REWRITE_TAC[REAL_LT_01; REAL_MUL_LID] THEN
REWRITE_TAC[REAL_OF_NUM_LT; LT_0] THEN
REWRITE_TAC[FACT; real_div; GSYM REAL_OF_NUM_MUL; real_pow] THEN
REWRITE_TAC[REAL_MUL_LID; REAL_INV_MUL] THEN
MATCH_MP_TAC(REAL_ARITH `(a = b) /\ c <= d ==> a <= c ==> b <= d`) THEN
CONJ_TAC THENL
[REWRITE_TAC[REAL_MUL_AC];
REWRITE_TAC[REAL_ADD_ASSOC; REAL_LE_RADD] THEN
GEN_REWRITE_TAC (RAND_CONV o LAND_CONV o LAND_CONV) [REAL_MUL_SYM] THEN
REWRITE_TAC[GSYM REAL_ADD_LDISTRIB; GSYM REAL_MUL_ASSOC] THEN
MATCH_MP_TAC REAL_LE_LMUL THEN CONJ_TAC THENL
[MATCH_MP_TAC REAL_LE_INV THEN REWRITE_TAC[REAL_OF_NUM_LE; LE_0];
MATCH_MP_TAC REAL_LE_ADD2 THEN CONJ_TAC THENL
[MATCH_MP_TAC REAL_LE_RMUL THEN CONJ_TAC THENL
[GEN_REWRITE_TAC RAND_CONV [REAL_ARITH `&2 = &1 + &1`] THEN
MATCH_MP_TAC REAL_LE_ADD2 THEN ASM_REWRITE_TAC[] THEN
MATCH_MP_TAC REAL_INV_LE_1 THEN REWRITE_TAC[REAL_LE_POW2];
MATCH_MP_TAC REAL_LE_TRANS THEN
EXISTS_TAC `abs(t - &2 pow n * (x pow i / &(FACT i)))` THEN
ASM_REWRITE_TAC[REAL_ABS_POS]];
REWRITE_TAC[REAL_ABS_MUL] THEN
GEN_REWRITE_TAC RAND_CONV [GSYM REAL_MUL_LID] THEN
MATCH_MP_TAC REAL_LE_MUL2 THEN REWRITE_TAC[REAL_ABS_POS] THEN
CONJ_TAC THENL
[REWRITE_TAC[REAL_ABS_POW] THEN MATCH_MP_TAC REAL_POW_1_LE THEN
ASM_REWRITE_TAC[REAL_ABS_POS];
MATCH_MP_TAC(REAL_ARITH `&0 <= a ==> abs(a) <= a`) THEN
MATCH_MP_TAC REAL_LE_INV THEN
REWRITE_TAC[REAL_OF_NUM_LE; LE_0]]]]]);;
let STEP_SIN = prove
(`abs(x) <= &1 /\
abs(s - &2 pow n * --(x pow 2)) <= &1 /\
abs(t - &2 pow n *
x pow (2 * i + 1) / &(FACT (2 * i + 1)))
<= &1 /\
&2 * abs(u * &2 pow n * &(2 * i + 2) * &(2 * i + 3)
- s * t)
<= &2 pow n * &(2 * i + 2) * &(2 * i + 3)
==> abs(u - &2 pow n *
--(x pow (2 * (SUC i) + 1)) /
&(FACT (2 * (SUC i) + 1))) <= &1`,
STRIP_TAC THEN
MP_TAC(SPECL [`n:num`; `s:real`; `t:real`; `u:real`;
`--(x pow 2)`;
`x pow (2 * i + 1) /
&(FACT(2 * i + 1))`;
`&1`; `&1`; `&1`;
`&(2 * i + 2) * &(2 * i + 3)`]
STEP_LEMMA2) THEN
ASM_REWRITE_TAC[REAL_LT_01; REAL_MUL_LID] THEN W(C SUBGOAL_THEN
(fun th -> REWRITE_TAC[th]) o funpow 2 (fst o dest_imp) o snd) THENL
[REWRITE_TAC(map num_CONV [`3`; `2`; `1`]) THEN
REWRITE_TAC[REAL_OF_NUM_MUL; REAL_OF_NUM_LT] THEN
REWRITE_TAC[ADD_CLAUSES; MULT_CLAUSES; LT_0]; ALL_TAC] THEN
MATCH_MP_TAC(REAL_ARITH `(a = b) /\ c <= d ==> a <= c ==> b <= d`) THEN
CONJ_TAC THENL
[AP_TERM_TAC THEN AP_TERM_TAC THEN AP_TERM_TAC THEN SUBGOAL_THEN
`2 * (SUC i) + 1 = SUC(SUC(2 * i + 1))`
SUBST1_TAC THENL
[GEN_REWRITE_TAC I [GSYM REAL_OF_NUM_EQ] THEN
REWRITE_TAC[ADD1; GSYM REAL_OF_NUM_MUL; GSYM REAL_OF_NUM_ADD] THEN
REAL_ARITH_TAC;
REWRITE_TAC[real_pow; FACT] THEN
REWRITE_TAC[ADD1; GSYM ADD_ASSOC] THEN
REWRITE_TAC[ARITH] THEN
REWRITE_TAC[real_div; REAL_INV_MUL; GSYM REAL_OF_NUM_MUL;
GSYM REAL_OF_NUM_ADD] THEN
REWRITE_TAC[REAL_MUL_LID; REAL_MUL_RNEG; REAL_MUL_LNEG] THEN
REWRITE_TAC[REAL_POW_2; REAL_MUL_AC]];
GEN_REWRITE_TAC RAND_CONV
[SYM(REAL_RAT_REDUCE_CONV `&1 / &3 + &1 / &6 + &1 / &2`)] THEN
REWRITE_TAC[REAL_ADD_ASSOC; REAL_LE_RADD] THEN
SUBGOAL_THEN `&1 / (&(2 * i + 2) * &(2 * i + 3))
<= &1 / &6` ASSUME_TAC THENL
[REWRITE_TAC[real_div; REAL_MUL_LID] THEN
MATCH_MP_TAC REAL_LE_INV2 THEN
CONV_TAC(LAND_CONV (EQT_INTRO o REAL_ARITH)) THEN REWRITE_TAC[] THEN
REWRITE_TAC[REAL_ARITH `&6 = &2 * &3`] THEN
REWRITE_TAC[REAL_OF_NUM_MUL; REAL_OF_NUM_LE] THEN
MATCH_MP_TAC LE_MULT2 THEN ONCE_REWRITE_TAC[ADD_SYM] THEN
REWRITE_TAC[LE_ADD]; ALL_TAC] THEN
REWRITE_TAC[SYM(REAL_RAT_REDUCE_CONV `&1 / &6 * &2`)] THEN
GEN_REWRITE_TAC (RAND_CONV o RAND_CONV) [GSYM REAL_MUL_RID] THEN
REWRITE_TAC[GSYM REAL_ADD_LDISTRIB] THEN
MATCH_MP_TAC REAL_LE_MUL2 THEN ASM_REWRITE_TAC[] THEN
REPEAT CONJ_TAC THENL
[REWRITE_TAC[real_div; REAL_MUL_LID; REAL_LE_INV_EQ] THEN
REWRITE_TAC[REAL_OF_NUM_MUL; REAL_POS];
MATCH_MP_TAC REAL_LE_ADD THEN
REWRITE_TAC[REAL_MUL_RID; REAL_ABS_POS] THEN
MATCH_MP_TAC REAL_LE_ADD THEN
REWRITE_TAC[real_div; REAL_MUL_LID; REAL_LE_INV_EQ; REAL_ABS_POS] THEN
MATCH_MP_TAC REAL_LT_IMP_LE THEN REWRITE_TAC[REAL_LT_POW2];
REWRITE_TAC[REAL_MUL_RID]] THEN
MATCH_MP_TAC REAL_LE_ADD2 THEN CONJ_TAC THENL
[GEN_REWRITE_TAC RAND_CONV [REAL_ARITH `&2 = &1 + &1`] THEN
MATCH_MP_TAC REAL_LE_ADD2 THEN CONJ_TAC THENL
[REWRITE_TAC[REAL_ABS_NEG; REAL_ABS_POW] THEN
MATCH_MP_TAC REAL_POW_1_LE THEN ASM_REWRITE_TAC[REAL_ABS_POS];
REWRITE_TAC[real_div; REAL_MUL_LID] THEN
MATCH_MP_TAC REAL_INV_LE_1 THEN REWRITE_TAC[REAL_LE_POW2]];
REWRITE_TAC[real_div; REAL_ABS_MUL] THEN
GEN_REWRITE_TAC RAND_CONV [GSYM REAL_MUL_RID] THEN
MATCH_MP_TAC REAL_LE_MUL2 THEN REWRITE_TAC[REAL_ABS_POS] THEN
CONJ_TAC THENL
[REWRITE_TAC[REAL_ABS_POW] THEN MATCH_MP_TAC REAL_POW_1_LE THEN
ASM_REWRITE_TAC[REAL_ABS_POS];
REWRITE_TAC[REAL_ABS_INV; REAL_ABS_NUM] THEN
MATCH_MP_TAC REAL_INV_LE_1 THEN
REWRITE_TAC[REAL_OF_NUM_LE; FACT_LE]]]]);;
let STEP_COS = prove
(`abs(x) <= &1 /\
abs(s - &2 pow n * --(x pow 2)) <= &1 /\
abs(t - &2 pow n *
x pow (2 * i) / &(FACT (2 * i)))
<= k /\
&2 * abs(u * &2 pow n * &(2 * i + 1) * &(2 * i + 2)
- s * t)
<= &2 pow n * &(2 * i + 1) * &(2 * i + 2)
==> abs(u - &2 pow n *
--(x pow (2 * (SUC i))) /
&(FACT (2 * (SUC i))))
<= (&2 * inv(&(2 * i + 1) * &(2 * i + 2))) * k
+ inv(&(FACT(2 * i + 2))) + &1 / &2`,
STRIP_TAC THEN
MP_TAC(SPECL [`n:num`; `s:real`; `t:real`; `u:real`;
`--(x pow 2)`;
`x pow (2 * i) /
&(FACT(2 * i))`;
`&1`; `k:real`; `&1`;
`&(2 * i + 1) * &(2 * i + 2)`]
STEP_LEMMA2) THEN
ASM_REWRITE_TAC[REAL_LT_01; REAL_MUL_LID] THEN W(C SUBGOAL_THEN
(fun th -> REWRITE_TAC[th]) o funpow 2 (fst o dest_imp) o snd) THENL
[REWRITE_TAC(map num_CONV [`3`; `2`; `1`]) THEN
REWRITE_TAC[REAL_OF_NUM_MUL; REAL_OF_NUM_LT] THEN
REWRITE_TAC[ADD_CLAUSES; MULT_CLAUSES; LT_0]; ALL_TAC] THEN
MATCH_MP_TAC(REAL_ARITH `(a = b) /\ c <= d ==> a <= c ==> b <= d`) THEN
CONJ_TAC THENL
[AP_TERM_TAC THEN AP_TERM_TAC THEN AP_TERM_TAC THEN SUBGOAL_THEN
`2 * (SUC i) = SUC(SUC(2 * i))`
SUBST1_TAC THENL
[GEN_REWRITE_TAC I [GSYM REAL_OF_NUM_EQ] THEN
REWRITE_TAC[ADD1; GSYM REAL_OF_NUM_MUL; GSYM REAL_OF_NUM_ADD] THEN
REAL_ARITH_TAC;
REWRITE_TAC[real_pow; FACT] THEN
REWRITE_TAC[ADD1; GSYM ADD_ASSOC] THEN
REWRITE_TAC[ARITH] THEN
REWRITE_TAC[real_div; REAL_INV_MUL; GSYM REAL_OF_NUM_MUL;
GSYM REAL_OF_NUM_ADD] THEN
REWRITE_TAC[REAL_MUL_LID; REAL_MUL_RNEG; REAL_MUL_LNEG] THEN
REWRITE_TAC[REAL_POW_2; REAL_MUL_AC]];
REWRITE_TAC[REAL_ADD_ASSOC; REAL_LE_RADD] THEN
MATCH_MP_TAC REAL_LE_ADD2 THEN CONJ_TAC THENL
[REWRITE_TAC[REAL_MUL_ASSOC] THEN
MATCH_MP_TAC REAL_LE_RMUL THEN CONJ_TAC THENL
[REWRITE_TAC[real_div; REAL_MUL_LID] THEN
GEN_REWRITE_TAC RAND_CONV [GSYM REAL_MUL_SYM] THEN
MATCH_MP_TAC REAL_LE_LMUL THEN CONJ_TAC THENL
[MATCH_MP_TAC REAL_LE_INV THEN
REWRITE_TAC[REAL_OF_NUM_MUL; REAL_POS];
GEN_REWRITE_TAC RAND_CONV [REAL_ARITH `&2 = &1 + &1`] THEN
MATCH_MP_TAC REAL_LE_ADD2 THEN CONJ_TAC THENL
[REWRITE_TAC[REAL_ABS_NEG; REAL_ABS_POW] THEN
MATCH_MP_TAC REAL_POW_1_LE THEN
ASM_REWRITE_TAC[REAL_ABS_POS];
MATCH_MP_TAC REAL_INV_LE_1 THEN REWRITE_TAC[REAL_LE_POW2]]];
MATCH_MP_TAC REAL_LE_TRANS THEN EXISTS_TAC
`abs(t - &2 pow n * x pow (2 * i) / &(FACT (2 * i)))` THEN
ASM_REWRITE_TAC[REAL_ABS_POS]];
REWRITE_TAC[real_div; REAL_MUL_LID; REAL_INV_MUL; REAL_ABS_MUL] THEN
GEN_REWRITE_TAC RAND_CONV [GSYM REAL_MUL_RID] THEN
ONCE_REWRITE_TAC[AC REAL_MUL_AC
`(a * b) * c * d = (d * a * b) * c`] THEN
MATCH_MP_TAC REAL_LE_MUL2 THEN REWRITE_TAC[REAL_ABS_POS] THEN
REPEAT CONJ_TAC THENL
[REPEAT(MATCH_MP_TAC REAL_LE_MUL THEN CONJ_TAC) THEN
REWRITE_TAC[REAL_POS; REAL_ABS_POS; REAL_LE_INV_EQ];
REWRITE_TAC[REAL_ABS_INV] THEN
REWRITE_TAC[GSYM REAL_INV_MUL; REAL_ABS_NUM] THEN
MATCH_MP_TAC REAL_EQ_IMP_LE THEN AP_TERM_TAC THEN
REWRITE_TAC[num_CONV `2`; num_CONV `1`; ADD_CLAUSES] THEN
REWRITE_TAC[SYM(num_CONV `2`); SYM(num_CONV `1`)] THEN
REWRITE_TAC[FACT; REAL_OF_NUM_MUL] THEN
REWRITE_TAC[MULT_AC];
REWRITE_TAC[REAL_ABS_POW] THEN MATCH_MP_TAC REAL_POW_1_LE THEN
ASM_REWRITE_TAC[REAL_ABS_POS]]]]);;
let STEP_LN = prove
(`2 <= n /\
abs(x) <= &1 / &2 /\
abs(s - &2 pow n * --x) <= &1 /\
abs(t - &2 pow n * -- ((--x) pow (SUC i) / &(SUC i))) <= &3 /\
&2 * abs(u * &2 pow n * &(SUC(SUC i)) - &(SUC i) * s * t)
<= &2 pow n * &(SUC(SUC i))
==> abs(u - &2 pow n * -- ((--x) pow (SUC(SUC i)) / &(SUC(SUC i)))) <= &3`,
STRIP_TAC THEN
MP_TAC(SPECL [`n:num`; `s:real`; `t:real`; `u:real`;
`--x`;
`-- (--x pow (SUC i) / &(SUC i))`;
`&1`; `&3`;
`&(SUC i)`;
`&(SUC(SUC i))`]
STEP_LEMMA2) THEN
ASM_REWRITE_TAC[REAL_LT_01; REAL_MUL_LID] THEN
REWRITE_TAC[REAL_OF_NUM_LT; LT_0] THEN
MATCH_MP_TAC(REAL_ARITH `(a = b) /\ c <= d ==> a <= c ==> b <= d`) THEN
CONJ_TAC THENL
[AP_TERM_TAC THEN AP_TERM_TAC THEN AP_TERM_TAC THEN
REWRITE_TAC[real_pow; real_div; REAL_INV_MUL] THEN
REWRITE_TAC[REAL_MUL_LNEG; REAL_MUL_RNEG; REAL_NEG_NEG] THEN
AP_TERM_TAC THEN REWRITE_TAC[REAL_MUL_ASSOC] THEN
GEN_REWRITE_TAC LAND_CONV [REAL_MUL_SYM] THEN
SUBGOAL_THEN `inv(&(SUC i)) * &(SUC i) = &1` ASSUME_TAC THENL
[MATCH_MP_TAC REAL_MUL_LINV THEN
REWRITE_TAC[REAL_OF_NUM_EQ; NOT_SUC];
ASM_REWRITE_TAC[REAL_MUL_ASSOC; REAL_MUL_LID] THEN
REWRITE_TAC[REAL_MUL_AC]];
GEN_REWRITE_TAC RAND_CONV [SYM(REAL_RAT_REDUCE_CONV
`(&1 / &2 + &1 / &4) * &3 + &1 / &4 + &1 / &2`)] THEN
REWRITE_TAC[REAL_ADD_ASSOC; REAL_LE_RADD] THEN
MATCH_MP_TAC REAL_LE_ADD2 THEN CONJ_TAC THENL
[REWRITE_TAC[REAL_MUL_ASSOC] THEN MATCH_MP_TAC REAL_LE_RMUL THEN
CONV_TAC(RAND_CONV (EQT_INTRO o REAL_ARITH)) THEN REWRITE_TAC[] THEN
GEN_REWRITE_TAC RAND_CONV [GSYM REAL_MUL_LID] THEN
MATCH_MP_TAC REAL_LE_MUL2 THEN REPEAT CONJ_TAC THENL
[MATCH_MP_TAC REAL_LE_RCANCEL_IMP THEN
EXISTS_TAC `&(SUC(SUC i))` THEN
REWRITE_TAC[REAL_MUL_LZERO; REAL_OF_NUM_LT; LT_0] THEN
REWRITE_TAC[real_div; GSYM REAL_MUL_ASSOC] THEN
MATCH_MP_TAC REAL_LE_MUL THEN REWRITE_TAC[REAL_POS] THEN
MATCH_MP_TAC(REAL_ARITH `(x = &1) ==> &0 <= x`) THEN
MATCH_MP_TAC REAL_MUL_LINV THEN
REWRITE_TAC[REAL_OF_NUM_EQ; NOT_SUC];
MATCH_MP_TAC REAL_LE_RCANCEL_IMP THEN
EXISTS_TAC `&(SUC(SUC i))` THEN
REWRITE_TAC[REAL_OF_NUM_LT; LT_0] THEN
REWRITE_TAC[real_div; REAL_MUL_LID; GSYM REAL_MUL_ASSOC] THEN
GEN_REWRITE_TAC RAND_CONV [GSYM REAL_MUL_RID] THEN
MATCH_MP_TAC REAL_LE_MUL2 THEN REWRITE_TAC[REAL_POS] THEN
REWRITE_TAC[REAL_OF_NUM_LE; LE] THEN
MATCH_MP_TAC(REAL_ARITH `(x = &1) ==> &0 <= x /\ x <= &1`) THEN
MATCH_MP_TAC REAL_MUL_LINV THEN
REWRITE_TAC[REAL_OF_NUM_EQ; NOT_SUC];
MATCH_MP_TAC REAL_LE_ADD THEN REWRITE_TAC[REAL_ABS_POS] THEN
REWRITE_TAC[real_div; REAL_MUL_LID; REAL_LE_INV_EQ] THEN
MATCH_MP_TAC REAL_LT_IMP_LE THEN REWRITE_TAC[REAL_LT_POW2];
MATCH_MP_TAC REAL_LE_ADD2 THEN ASM_REWRITE_TAC[REAL_ABS_NEG] THEN
REWRITE_TAC[real_div; REAL_MUL_LID] THEN
MATCH_MP_TAC REAL_LE_INV2 THEN
CONV_TAC(LAND_CONV (EQT_INTRO o REAL_ARITH)) THEN REWRITE_TAC[] THEN
SUBST1_TAC(SYM(REAL_INT_REDUCE_CONV `&2 pow 2`)) THEN
MATCH_MP_TAC REAL_MONO_POW2 THEN ASM_REWRITE_TAC[]];
REWRITE_TAC[real_div; REAL_ABS_MUL; REAL_ABS_NEG; REAL_ABS_INV] THEN
REWRITE_TAC[REAL_ABS_POW; REAL_ABS_NEG; REAL_MUL_LID] THEN
REWRITE_TAC[REAL_ABS_NUM] THEN REWRITE_TAC[GSYM REAL_MUL_ASSOC] THEN
ONCE_REWRITE_TAC[REAL_MUL_SYM] THEN REWRITE_TAC[REAL_MUL_ASSOC] THEN
SUBGOAL_THEN `inv(&(SUC i)) * &(SUC i) = &1` ASSUME_TAC THENL
[MATCH_MP_TAC REAL_MUL_LINV THEN REWRITE_TAC[REAL_OF_NUM_EQ; NOT_SUC];
GEN_REWRITE_TAC RAND_CONV
[EQT_ELIM(REAL_RAT_REDUCE_CONV `inv(&4) = inv(&2) * inv(&2)`)] THEN
ASM_REWRITE_TAC[REAL_MUL_RID; GSYM REAL_MUL_ASSOC] THEN
MATCH_MP_TAC REAL_LE_MUL2 THEN REWRITE_TAC
[REAL_POS; REAL_ABS_POS; REAL_LE_INV_EQ; GSYM REAL_ABS_POW] THEN
CONJ_TAC THENL
[MATCH_MP_TAC REAL_LE_INV2 THEN REWRITE_TAC[REAL_POS] THEN
REWRITE_TAC[ADD1; GSYM REAL_OF_NUM_ADD] THEN
MP_TAC(SPEC `i:num` REAL_POS) THEN REAL_ARITH_TAC;
REWRITE_TAC[real_pow; REAL_ABS_POW] THEN
GEN_REWRITE_TAC RAND_CONV [GSYM REAL_MUL_RID] THEN
MATCH_MP_TAC REAL_LE_MUL2 THEN
REWRITE_TAC[REAL_LE_INV_EQ; REAL_ABS_POS] THEN
REPEAT CONJ_TAC THENL
[CONV_TAC(RAND_CONV REAL_RAT_REDUCE_CONV) THEN ASM_REWRITE_TAC[];
MATCH_MP_TAC REAL_POW_LE THEN REWRITE_TAC[REAL_ABS_POS];
MATCH_MP_TAC REAL_POW_1_LE THEN REWRITE_TAC[REAL_ABS_POS] THEN
MATCH_MP_TAC REAL_LE_TRANS THEN EXISTS_TAC `&1 / &2` THEN
ASM_REWRITE_TAC[] THEN CONV_TAC REAL_RAT_REDUCE_CONV]]]]]);;
(* ------------------------------------------------------------------------- *)
(* Expand the "!k. SUC k < r ==> P k" term for given numeral r. *)
(* ------------------------------------------------------------------------- *)
let EXPAND_RANGE_CONV =
let pth0 = prove
(`(!k. SUC k < 0 ==> P k) <=> T`,
REWRITE_TAC[LT])
and pth1 = prove
(`(!k. k < (SUC m) ==> P k) <=>
(!k. k < m ==> P k) /\ P m`,
REWRITE_TAC[LT] THEN MESON_TAC[])
and pth2 = prove
(`(!k. k < 0 ==> P k) <=> T`,
REWRITE_TAC[LT]) in
let triv_conv = GEN_REWRITE_CONV I [pth0]
and trivial_conv = GEN_REWRITE_CONV I [pth2]
and nontrivial_conv = GEN_REWRITE_CONV I [pth1] in
let s_tm = `s:real`
and m_tm = `m:num`
and n_tm = `n:num` in
let rec expand_conv tm =
try trivial_conv tm
with Failure _ ->
let mth = num_CONV(rand(lhand(body(rand tm)))) in
let th1 = BINDER_CONV(LAND_CONV(RAND_CONV(K mth))) tm in
let th2 = TRANS th1 (nontrivial_conv (rand(concl th1))) in
let th3 = COMB2_CONV (RAND_CONV expand_conv) (SUBS_CONV[SYM mth])
(rand(concl th2)) in
TRANS th2 th3 in
let hack_conv =
triv_conv ORELSEC
(BINDER_CONV (LAND_CONV
((RAND_CONV num_CONV) THENC REWR_CONV LT_SUC)) THENC
expand_conv) in
hack_conv;;
(* ------------------------------------------------------------------------- *)
(* Lemmas leading to iterative versions. *)
(* ------------------------------------------------------------------------- *)
let STEP_EXP_THM = prove
(`abs(x) <= &1 /\
abs(s - &2 pow n * x) < &1 /\
abs(t(i) - &2 pow n * (x pow i / &(FACT i))) <= k ==>
&2 * abs(t(SUC i) * &2 pow n * &(SUC i) - s * t(i)) <= &2 pow n * &(SUC i)
==> abs(t(SUC i) - &2 pow n * (x pow (SUC i)) / &(FACT(SUC i))) <=
(&2 / &(SUC i)) * k + &1 / &(FACT(SUC i)) + &1 / &2`,
REPEAT STRIP_TAC THEN MATCH_MP_TAC(GEN_ALL STEP_EXP) THEN
MAP_EVERY EXISTS_TAC [`s:real`; `t(i:num):real`] THEN
ASM_REWRITE_TAC[] THEN MATCH_MP_TAC REAL_LT_IMP_LE THEN
ASM_REWRITE_TAC[]);;
let STEP_EXP_RULE th =
let th1 = MATCH_MP STEP_EXP_THM th in
let th2 = UNDISCH(PURE_REWRITE_RULE[ARITH_SUC] th1) in
let th3 = CONV_RULE(RAND_CONV(ONCE_DEPTH_CONV NUM_FACT_CONV)) th2 in
let th4 = CONV_RULE(RAND_CONV REAL_RAT_REDUCE_CONV) th3 in
let th5 = ASSUME(find is_conj (hyp th)) in
let th6a,th6b = (I F_F CONJUNCT1) (CONJ_PAIR th5) in
CONJ th6a (CONJ th6b th4);;
let STEP_EXP_0 = (UNDISCH o prove)
(`abs(x) <= &1 /\
abs(s - &2 pow n * x) < &1 /\
(t(0) = &2 pow n) ==>
abs(x) <= &1 /\
abs(s - &2 pow n * x) < &1 /\
abs(t(0) - &2 pow n * (x pow 0 / &(FACT 0))) <= &0`,
STRIP_TAC THEN ASM_REWRITE_TAC[] THEN
REWRITE_TAC[real_pow; FACT; real_div; REAL_INV_1; REAL_MUL_RID] THEN
REWRITE_TAC[REAL_SUB_REFL; REAL_ABS_0; REAL_LE_REFL]);;
let STEP_EXP_1 = STEP_EXP_RULE STEP_EXP_0;; (* e(1) = 3/2 *)
let STEP_EXP_2 = STEP_EXP_RULE STEP_EXP_1;; (* e(2) = 5/2 *)
let STEP_EXP_3 = STEP_EXP_RULE STEP_EXP_2;; (* e(3) = 7/3 *)
let STEP_EXP_4 = STEP_EXP_RULE STEP_EXP_3;; (* e(4) = 41/24 *)
let STEP_EXP_5 = STEP_EXP_RULE STEP_EXP_4;; (* e(5) = 143/120 *)
let STEP_EXP_4_PLUS = prove
(`4 <= m /\
abs(x) <= &1 /\
abs(s - &2 pow n * x) < &1 /\
(t(0) = &2 pow n) /\
(!k. SUC k < SUC m ==>
&2 * abs(t(SUC k) * &2 pow n * &(SUC k) - s * t(k))
<= &2 pow n * &(SUC k))
==> abs(t m - &2 pow n * x pow m / &(FACT m)) <= &2`,
let lemma = prove
(`(!k. k < (SUC m) ==> P k) <=>
(!k. k < m ==> P k) /\ P m`,
REWRITE_TAC[LT] THEN MESON_TAC[]) in
DISCH_THEN(CONJUNCTS_THEN2 ASSUME_TAC MP_TAC) THEN
POP_ASSUM(X_CHOOSE_THEN `d:num` SUBST1_TAC o REWRITE_RULE[LE_EXISTS]) THEN
DISCH_THEN(CONJUNCTS_THEN2 ASSUME_TAC MP_TAC) THEN
DISCH_THEN(CONJUNCTS_THEN2 ASSUME_TAC MP_TAC) THEN
DISCH_THEN(CONJUNCTS_THEN2 ASSUME_TAC MP_TAC) THEN
REWRITE_TAC[LT_SUC] THEN SPEC_TAC(`d:num`,`d:num`) THEN
INDUCT_TAC THENL
[REWRITE_TAC[ADD_CLAUSES] THEN
SUBST1_TAC(TOP_DEPTH_CONV num_CONV `4`) THEN
REWRITE_TAC[lemma] THEN REWRITE_TAC[ARITH_SUC] THEN
REWRITE_TAC[LT] THEN STRIP_TAC THEN
MP_TAC (DISCH_ALL STEP_EXP_4) THEN ASM_REWRITE_TAC[] THEN
MATCH_MP_TAC(REAL_ARITH `b <= c ==> a <= b ==> a <= c`) THEN
CONV_TAC REAL_RAT_REDUCE_CONV;
REWRITE_TAC[ADD_CLAUSES; lemma] THEN STRIP_TAC THEN
MATCH_MP_TAC REAL_LE_TRANS THEN
EXISTS_TAC `&2 / &(SUC(4 + d)) * &2 +
&1 / &(FACT(SUC(4 + d))) + &1 / &2` THEN
CONJ_TAC THENL
[MATCH_MP_TAC(GEN_ALL STEP_EXP) THEN ASM_REWRITE_TAC[] THEN
EXISTS_TAC `s:real` THEN EXISTS_TAC `t(4 + d):real` THEN
ASM_REWRITE_TAC[] THEN CONJ_TAC THENL
[MATCH_MP_TAC REAL_LT_IMP_LE THEN ASM_REWRITE_TAC[];
FIRST_ASSUM MATCH_MP_TAC THEN ASM_REWRITE_TAC[]];
GEN_REWRITE_TAC RAND_CONV
[SYM(REAL_RAT_REDUCE_CONV `&3 / &2 + &1 / &2`)] THEN
REWRITE_TAC[REAL_LE_RADD; REAL_ADD_ASSOC] THEN
MATCH_MP_TAC REAL_LE_TRANS THEN EXISTS_TAC `&4 / &5 + &1 / &120` THEN
CONV_TAC(RAND_CONV REAL_RAT_REDUCE_CONV) THEN REWRITE_TAC[] THEN
MATCH_MP_TAC REAL_LE_ADD2 THEN CONJ_TAC THENL
[ONCE_REWRITE_TAC[REAL_MUL_SYM] THEN
REWRITE_TAC[real_div; REAL_MUL_ASSOC] THEN
REWRITE_TAC[REAL_ARITH `&2 * &2 = &4`] THEN
MATCH_MP_TAC REAL_LE_LMUL THEN
REWRITE_TAC[REAL_ARITH `&0 <= &4`] THEN
MATCH_MP_TAC REAL_LE_INV2 THEN
REWRITE_TAC[ADD1; GSYM REAL_OF_NUM_ADD] THEN
MP_TAC(SPEC `d':num` REAL_POS) THEN REAL_ARITH_TAC;
REWRITE_TAC[real_div; REAL_MUL_LID] THEN
MATCH_MP_TAC REAL_LE_INV2 THEN
CONV_TAC(LAND_CONV (EQT_INTRO o REAL_ARITH)) THEN REWRITE_TAC[] THEN
SUBST1_TAC(SYM(NUM_FACT_CONV `FACT 5`)) THEN
REWRITE_TAC[REAL_OF_NUM_LE] THEN MATCH_MP_TAC FACT_MONO THEN
REWRITE_TAC[num_CONV `5`; LE_SUC; LE_ADD]]]]);;
let STEPS_EXP_0 = prove
(`abs(x) <= &1 /\
abs(s - &2 pow n * x) < &1 /\
(t(0) = &2 pow n) /\
(!k. SUC k < 0 ==>
&2 * abs(t(SUC k) * &2 pow n * &(SUC k) - s * t(k))
<= &2 pow n * &(SUC k))
==> abs(sum(0,0) t -
&2 pow n * sum(0,0) (\i. x pow i / &(FACT i))) <= &2 * &0`,
STRIP_TAC THEN ASM_REWRITE_TAC[sum] THEN
REWRITE_TAC[REAL_MUL_RZERO; REAL_ABS_0; REAL_SUB_REFL; REAL_LE_REFL]);;
let STEPS_EXP_1 = prove
(`abs(x) <= &1 /\
abs(s - &2 pow n * x) < &1 /\
(t(0) = &2 pow n) /\
(!k. SUC k < 1 ==>
&2 * abs(t(SUC k) * &2 pow n * &(SUC k) - s * t(k))
<= &2 pow n * &(SUC k))
==> abs(sum(0,1) t - &2 pow n * sum(0,1)(\i. x pow i / &(FACT i)))
<= &2 * &1`,
CONV_TAC(ONCE_DEPTH_CONV EXPAND_RANGE_CONV) THEN REWRITE_TAC[] THEN
STRIP_TAC THEN CONV_TAC(ONCE_DEPTH_CONV REAL_SUM_CONV) THEN
MATCH_MP_TAC REAL_LE_TRANS THEN EXISTS_TAC `&0` THEN
CONV_TAC(RAND_CONV REAL_RAT_REDUCE_CONV) THEN REWRITE_TAC[] THEN
MP_TAC (DISCH_ALL STEP_EXP_0) THEN ASM_REWRITE_TAC[]);;
let STEPS_EXP_2 = prove
(`abs(x) <= &1 /\
abs(s - &2 pow n * x) < &1 /\
(t(0) = &2 pow n) /\
(!k. SUC k < 2 ==>
&2 * abs(t(SUC k) * &2 pow n * &(SUC k) - s * t(k))
<= &2 pow n * &(SUC k))
==> abs(sum(0,2) t - &2 pow n * sum(0,2) (\i. x pow i / &(FACT i)))
<= &2 * &2`,
CONV_TAC(ONCE_DEPTH_CONV EXPAND_RANGE_CONV) THEN REWRITE_TAC[] THEN
STRIP_TAC THEN CONV_TAC(ONCE_DEPTH_CONV REAL_SUM_CONV) THEN
REWRITE_TAC[REAL_ADD_LDISTRIB] THEN
REWRITE_TAC[REAL_ARITH `(a + b) - (c + d) = (a - c) + (b - d)`] THEN
MATCH_MP_TAC REAL_LE_TRANS THEN EXISTS_TAC `&0 + &3 / &2` THEN
CONV_TAC(RAND_CONV REAL_RAT_REDUCE_CONV) THEN REWRITE_TAC[] THEN
MATCH_MP_TAC(REAL_LE_IMP(REAL_ARITH `abs(a + b) <= abs(a) + abs(b)`)) THEN
MATCH_MP_TAC REAL_LE_ADD2 THEN CONJ_TAC THENL
[MP_TAC (DISCH_ALL STEP_EXP_0) THEN ASM_REWRITE_TAC[];
MP_TAC (DISCH_ALL STEP_EXP_1) THEN
ASM_REWRITE_TAC[ADD_CLAUSES]]);;
let STEPS_EXP_3 = prove
(`abs(x) <= &1 /\
abs(s - &2 pow n * x) < &1 /\
(t(0) = &2 pow n) /\
(!k. SUC k < 3 ==>
&2 * abs(t(SUC k) * &2 pow n * &(SUC k) - s * t(k))
<= &2 pow n * &(SUC k))
==> abs(sum(0,3) t - &2 pow n * sum(0,3) (\i. x pow i / &(FACT i)))
<= &2 * &3`,
CONV_TAC(ONCE_DEPTH_CONV EXPAND_RANGE_CONV) THEN REWRITE_TAC[] THEN
STRIP_TAC THEN CONV_TAC(ONCE_DEPTH_CONV REAL_SUM_CONV) THEN
REWRITE_TAC[REAL_ADD_LDISTRIB] THEN
REWRITE_TAC[REAL_ARITH `(a + b) - (c + d) = (a - c) + (b - d)`] THEN
REWRITE_TAC[GSYM REAL_ADD_ASSOC] THEN
MATCH_MP_TAC REAL_LE_TRANS THEN EXISTS_TAC `&0 + &3 / &2 + &5 / &2` THEN
CONV_TAC(RAND_CONV REAL_RAT_REDUCE_CONV) THEN REWRITE_TAC[] THEN
REPEAT
(MATCH_MP_TAC(REAL_LE_IMP(REAL_ARITH `abs(a + b) <= abs(a) + abs(b)`)) THEN
MATCH_MP_TAC REAL_LE_ADD2 THEN CONJ_TAC)
THENL
[MP_TAC (DISCH_ALL STEP_EXP_0) THEN ASM_REWRITE_TAC[];
MP_TAC (DISCH_ALL STEP_EXP_1) THEN ASM_REWRITE_TAC[ADD_CLAUSES];
MP_TAC (DISCH_ALL STEP_EXP_2) THEN ASM_REWRITE_TAC[ADD_CLAUSES]]);;
let STEPS_EXP_4 = prove
(`abs(x) <= &1 /\
abs(s - &2 pow n * x) < &1 /\
(t(0) = &2 pow n) /\
(!k. SUC k < 4 ==>
&2 * abs(t(SUC k) * &2 pow n * &(SUC k) - s * t(k))
<= &2 pow n * &(SUC k))
==> abs(sum(0,4) t - &2 pow n * sum(0,4) (\i. x pow i / &(FACT i)))
<= &2 * &4`,
CONV_TAC(ONCE_DEPTH_CONV EXPAND_RANGE_CONV) THEN REWRITE_TAC[] THEN
STRIP_TAC THEN CONV_TAC(ONCE_DEPTH_CONV REAL_SUM_CONV) THEN
REWRITE_TAC[REAL_ADD_LDISTRIB] THEN
REWRITE_TAC[REAL_ARITH `(a + b) - (c + d) = (a - c) + (b - d)`] THEN
REWRITE_TAC[GSYM REAL_ADD_ASSOC] THEN
MATCH_MP_TAC REAL_LE_TRANS THEN
EXISTS_TAC `&0 + &3 / &2 + &5 / &2 + &7 / &3` THEN
CONV_TAC(RAND_CONV REAL_RAT_REDUCE_CONV) THEN REWRITE_TAC[] THEN
REPEAT
(MATCH_MP_TAC(REAL_LE_IMP(REAL_ARITH `abs(a + b) <= abs(a) + abs(b)`)) THEN
MATCH_MP_TAC REAL_LE_ADD2 THEN CONJ_TAC)
THENL
[MP_TAC (DISCH_ALL STEP_EXP_0) THEN ASM_REWRITE_TAC[];
MP_TAC (DISCH_ALL STEP_EXP_1) THEN ASM_REWRITE_TAC[ADD_CLAUSES];
MP_TAC (DISCH_ALL STEP_EXP_2) THEN ASM_REWRITE_TAC[ADD_CLAUSES];
MP_TAC (DISCH_ALL STEP_EXP_3) THEN ASM_REWRITE_TAC[ADD_CLAUSES]]);;
(* ------------------------------------------------------------------------- *)
(* Iterated versions. *)
(* ------------------------------------------------------------------------- *)
let STEPS_EXP_LEMMA = prove
(`(!k. P(SUC k) ==> P(k)) /\
(P(0) ==> (abs(sum(0,0) z) <= &2 * &0)) /\
(P(1) ==> (abs(sum(0,1) z) <= &2 * &1)) /\
(P(2) ==> (abs(sum(0,2) z) <= &2 * &2)) /\
(P(3) ==> (abs(sum(0,3) z) <= &2 * &3)) /\
(P(4) ==> (abs(sum(0,4) z) <= &2 * &4)) /\
(!m. 4 <= m /\ P(SUC m) ==> (abs(z m) <= &2))
==> !m. P(m) ==> (abs(sum(0,m) z) <= &2 * &m)`,
STRIP_TAC THEN SUBGOAL_THEN
`!d. P(d + 4) ==>
abs(sum(0,d + 4) z) <= &2 * &(d + 4)`
ASSUME_TAC THENL
[INDUCT_TAC THEN ASM_REWRITE_TAC[ADD_CLAUSES] THEN
DISCH_TAC THEN REWRITE_TAC[sum; ADD1] THEN
ONCE_REWRITE_TAC[GSYM REAL_OF_NUM_ADD] THEN
REWRITE_TAC[REAL_ADD_LDISTRIB] THEN
MATCH_MP_TAC(REAL_LE_IMP(REAL_ARITH `abs(a + b) <= abs(a) + abs(b)`)) THEN
MATCH_MP_TAC REAL_LE_ADD2 THEN CONJ_TAC THENL
[FIRST_ASSUM MATCH_MP_TAC THEN ASM_REWRITE_TAC[] THEN
FIRST_ASSUM MATCH_MP_TAC THEN ASM_REWRITE_TAC[];
REWRITE_TAC[REAL_MUL_RID] THEN FIRST_ASSUM MATCH_MP_TAC THEN
ASM_REWRITE_TAC[ADD_CLAUSES] THEN ONCE_REWRITE_TAC[ADD_SYM] THEN
REWRITE_TAC[LE_ADD]];
GEN_TAC THEN
DISJ_CASES_THEN MP_TAC (SPECL [`4`; `m:num`] LE_CASES) THENL
[DISCH_THEN(CHOOSE_THEN SUBST1_TAC o REWRITE_RULE[LE_EXISTS]) THEN
ONCE_REWRITE_TAC[ADD_SYM] THEN ASM_REWRITE_TAC[];
SUBST1_TAC(TOP_DEPTH_CONV num_CONV `4`) THEN
REWRITE_TAC[LE] THEN REWRITE_TAC[ARITH_SUC] THEN
DISCH_THEN(REPEAT_TCL DISJ_CASES_THEN SUBST1_TAC) THEN
ASM_REWRITE_TAC[]]]);;
let STEPS_EXP = prove
(`abs(x) <= &1 /\
abs(s - &2 pow n * x) < &1 /\
(t(0) = &2 pow n) /\
(!k. SUC k < m ==>
&2 * abs(t(SUC k) * &2 pow n * &(SUC k) - s * t(k))
<= &2 pow n * &(SUC k))
==> abs(sum(0,m) t - &2 pow n * sum(0,m) (\i. x pow i / &(FACT i)))
<= &2 * &m`,
REWRITE_TAC[REAL_MUL_RSUM0; REAL_SUB_SUM0] THEN
SPEC_TAC(`m:num`,`m:num`) THEN MATCH_MP_TAC STEPS_EXP_LEMMA THEN
REWRITE_TAC[GSYM REAL_SUB_SUM0; GSYM REAL_MUL_RSUM0] THEN
REWRITE_TAC[STEPS_EXP_0; STEPS_EXP_1; STEPS_EXP_2; STEPS_EXP_3] THEN
REWRITE_TAC[STEPS_EXP_4; STEP_EXP_4_PLUS] THEN
GEN_TAC THEN STRIP_TAC THEN ASM_REWRITE_TAC[] THEN
GEN_TAC THEN DISCH_TAC THEN FIRST_ASSUM MATCH_MP_TAC THEN
MATCH_MP_TAC LT_TRANS THEN EXISTS_TAC `k:num` THEN
ASM_REWRITE_TAC[] THEN REWRITE_TAC[LT]);;
let STEPS_LN = prove
(`2 <= n /\
abs(x) <= &1 / &2 /\
abs(s - &2 pow n * --x) < &1 /\
(t(0) = --s) /\
(!k. SUC k < m ==>
&2 * abs(t(SUC k) * &2 pow n * &(SUC(SUC k))
- &(SUC k) * s * t(k))
<= &2 pow n * &(SUC(SUC k)))
==> abs(sum(0,m) t - &2 pow n * sum(0,m)
(\i. (--(&1)) pow i * x pow (SUC i) / &(SUC i))) <= &3 * &m`,
REWRITE_TAC[REAL_MUL_RSUM0; REAL_SUB_SUM0] THEN
STRIP_TAC THEN GEN_REWRITE_TAC RAND_CONV [REAL_MUL_SYM] THEN
MATCH_MP_TAC (REAL_LE_IMP SUM_ABS_LE) THEN
MATCH_MP_TAC SUM_BOUND THEN REWRITE_TAC[ADD_CLAUSES; LE_0] THEN
INDUCT_TAC THENL
[REWRITE_TAC[real_pow; ARITH; REAL_DIV_1; REAL_MUL_LID; REAL_MUL_RID] THEN
DISCH_TAC THEN ASM_REWRITE_TAC[] THEN
REWRITE_TAC[REAL_ARITH `-- a - b * c = --(a - b * --c)`] THEN
MATCH_MP_TAC REAL_LE_TRANS THEN EXISTS_TAC `&1` THEN
ASM_SIMP_TAC[REAL_ABS_NEG; REAL_LT_IMP_LE; REAL_OF_NUM_LE; ARITH];
ALL_TAC] THEN
DISCH_THEN(fun th -> ASSUME_TAC th THEN MP_TAC th) THEN
DISCH_THEN(ANTE_RES_THEN MP_TAC) THEN
SUBGOAL_THEN `p:num < m` (ANTE_RES_THEN MP_TAC) THENL
[UNDISCH_TAC `SUC p < m` THEN ARITH_TAC; ALL_TAC] THEN
DISCH_TAC THEN DISCH_TAC THEN
MATCH_MP_TAC(REAL_ARITH
`!y. abs(x - y) + abs(y - z) <= e ==> abs(x - z) <= e`) THEN
EXISTS_TAC `&(SUC p) * s * t p / (&2 pow n * &(SUC(SUC p)))` THEN
ONCE_REWRITE_TAC [SYM(REAL_RAT_REDUCE_CONV `&1 / &2 + &5 / &2`)] THEN
MATCH_MP_TAC REAL_LE_ADD2 THEN CONJ_TAC THENL
[MATCH_MP_TAC REAL_LE_RCANCEL_IMP THEN
EXISTS_TAC `&2 pow n * &(SUC(SUC p))` THEN
SUBGOAL_THEN `&0 < &2 pow n * &(SUC(SUC p))` ASSUME_TAC THENL
[MATCH_MP_TAC REAL_LT_MUL THEN
SIMP_TAC[REAL_POW_LT; REAL_OF_NUM_LT; LT_0; ARITH]; ALL_TAC] THEN
ASM_REWRITE_TAC[] THEN
SUBGOAL_THEN `!x y. &0 < y ==> (abs(x) * y = abs(x * y))`
(fun th -> ASM_SIMP_TAC[th]) THENL
[REPEAT STRIP_TAC THEN REWRITE_TAC[REAL_ABS_MUL] THEN
AP_TERM_TAC THEN ASM_SIMP_TAC[real_abs; REAL_LT_IMP_LE]; ALL_TAC] THEN
MATCH_MP_TAC REAL_LE_LCANCEL_IMP THEN EXISTS_TAC `&2` THEN
REWRITE_TAC[REAL_MUL_ASSOC] THEN CONV_TAC REAL_RAT_REDUCE_CONV THEN
REWRITE_TAC[GSYM REAL_MUL_ASSOC; REAL_MUL_LID] THEN
REWRITE_TAC[REAL_SUB_RDISTRIB] THEN
SUBGOAL_THEN `!a b c d. &0 < a ==> ((b * c * d / a) * a = b * c * d)`
(fun th -> ASM_SIMP_TAC[th]) THEN
SIMP_TAC[real_div; GSYM REAL_MUL_ASSOC; REAL_MUL_LINV; REAL_MUL_RID;
REAL_LT_IMP_NZ];
ALL_TAC] THEN
MATCH_MP_TAC(REAL_ARITH
`!y. abs(x - y) + abs(y - z) <= e ==> abs(x - z) <= e`) THEN
EXISTS_TAC `--(&1) pow p * s * x pow (SUC p) / &(SUC(SUC p))` THEN
ONCE_REWRITE_TAC [SYM(REAL_RAT_REDUCE_CONV `&9 / &4 + &1 / &4`)] THEN
MATCH_MP_TAC REAL_LE_ADD2 THEN CONJ_TAC THENL
[SUBGOAL_THEN `--(&1) pow p * s * x pow (SUC p) / &(SUC(SUC p)) =
&(SUC p) * s *
(&2 pow n * --(&1) pow p * x pow SUC p / &(SUC p)) /
(&2 pow n * &(SUC (SUC p)))`
SUBST1_TAC THENL
[REWRITE_TAC[real_div; GSYM REAL_MUL_ASSOC; REAL_INV_MUL] THEN
ONCE_REWRITE_TAC[AC REAL_MUL_AC
`a * b * c * d * e * f * g * h =
d * b * e * h * (g * c) * (f * a)`] THEN
SIMP_TAC[REAL_MUL_LINV; REAL_POW_EQ_0; REAL_OF_NUM_EQ;
ARITH; NOT_SUC] THEN
REWRITE_TAC[REAL_MUL_RID]; ALL_TAC] THEN
REWRITE_TAC[GSYM REAL_SUB_LDISTRIB; REAL_ABS_MUL] THEN
REWRITE_TAC[real_div; REAL_MUL_ASSOC; GSYM REAL_SUB_RDISTRIB] THEN
REWRITE_TAC[REAL_ABS_MUL; GSYM REAL_MUL_ASSOC] THEN
REWRITE_TAC[GSYM real_div] THEN
ONCE_REWRITE_TAC[AC REAL_MUL_AC `a * b * c * d = (a * b * d) * c`] THEN
GEN_REWRITE_TAC (LAND_CONV o LAND_CONV o REDEPTH_CONV)
[GSYM REAL_ABS_MUL] THEN
MATCH_MP_TAC REAL_LE_TRANS THEN
EXISTS_TAC `abs (&(SUC p) * s * inv (&2 pow n * &(SUC (SUC p)))) * &3` THEN
ASM_SIMP_TAC[REAL_LE_LMUL; REAL_ABS_POS] THEN
REWRITE_TAC[REAL_ABS_MUL; REAL_ABS_NUM; REAL_ABS_INV; REAL_ABS_POW] THEN
REWRITE_TAC[REAL_INV_MUL] THEN
REWRITE_TAC[GSYM REAL_MUL_ASSOC] THEN
ONCE_REWRITE_TAC[AC REAL_MUL_AC `a * b * c * d * e =
(d * a) * (b * c) * e`] THEN
MATCH_MP_TAC REAL_LE_TRANS THEN
EXISTS_TAC `inv(&1) * &3 / &4 * &3` THEN
CONV_TAC(RAND_CONV REAL_RAT_REDUCE_CONV) THEN REWRITE_TAC[] THEN
REWRITE_TAC[REAL_MUL_ASSOC] THEN MATCH_MP_TAC REAL_LE_RMUL THEN
REWRITE_TAC[REAL_OF_NUM_LE; ARITH] THEN
ONCE_REWRITE_TAC[GSYM REAL_MUL_ASSOC] THEN
MATCH_MP_TAC REAL_LE_MUL2 THEN
SIMP_TAC[REAL_LE_MUL; REAL_LE_INV_EQ; REAL_POS;
REAL_POW_LE; REAL_ABS_POS] THEN
CONJ_TAC THENL
[MATCH_MP_TAC REAL_LE_LCANCEL_IMP THEN
EXISTS_TAC `&(SUC(SUC p))` THEN
SIMP_TAC[REAL_MUL_ASSOC; REAL_MUL_RINV; REAL_OF_NUM_EQ; NOT_SUC] THEN
REWRITE_TAC[REAL_INV_1; REAL_MUL_LID; REAL_MUL_RID] THEN
REWRITE_TAC[REAL_OF_NUM_LT; REAL_OF_NUM_LE] THEN ARITH_TAC;
MATCH_MP_TAC REAL_LE_RCANCEL_IMP THEN
EXISTS_TAC `&2 pow n` THEN REWRITE_TAC[GSYM REAL_MUL_ASSOC] THEN
SIMP_TAC[REAL_MUL_LINV; REAL_POW_EQ_0; REAL_OF_NUM_EQ; ARITH_EQ] THEN
SIMP_TAC[REAL_POW_LT; REAL_OF_NUM_LT; ARITH; REAL_MUL_RID] THEN
MATCH_MP_TAC(REAL_ARITH
`!y. abs(x - y) < &1 /\ abs(y) <= d - &1 ==> abs(x) <= d`) THEN
EXISTS_TAC `&2 pow n * --x` THEN ASM_REWRITE_TAC[] THEN
MATCH_MP_TAC REAL_LE_RCANCEL_IMP THEN EXISTS_TAC `inv(&2 pow n)` THEN
SIMP_TAC[REAL_LT_INV_EQ; REAL_POW_LT; REAL_OF_NUM_LT; ARITH] THEN
REWRITE_TAC[REAL_ABS_MUL; REAL_ABS_NEG; REAL_ABS_POW; REAL_ABS_NUM] THEN
GEN_REWRITE_TAC LAND_CONV [REAL_MUL_SYM] THEN
SIMP_TAC[REAL_MUL_ASSOC; REAL_MUL_LINV; REAL_POW_EQ_0; REAL_OF_NUM_EQ;
ARITH_EQ] THEN
REWRITE_TAC[REAL_MUL_LID] THEN MATCH_MP_TAC REAL_LE_TRANS THEN
EXISTS_TAC `&1 / &2` THEN ASM_REWRITE_TAC[] THEN
REWRITE_TAC[real_div; REAL_SUB_RDISTRIB; GSYM REAL_MUL_ASSOC] THEN
SIMP_TAC[REAL_MUL_RINV; REAL_POW_EQ_0; REAL_OF_NUM_EQ; ARITH_EQ] THEN
REWRITE_TAC[REAL_MUL_LID; REAL_MUL_RID] THEN
REWRITE_TAC[REAL_LE_SUB_LADD] THEN ONCE_REWRITE_TAC[REAL_ADD_SYM] THEN
REWRITE_TAC[GSYM REAL_LE_SUB_LADD] THEN
CONV_TAC REAL_RAT_REDUCE_CONV THEN
REWRITE_TAC[real_div; REAL_MUL_LID] THEN
MATCH_MP_TAC REAL_LE_INV2 THEN
REWRITE_TAC[REAL_OF_NUM_LT; ARITH] THEN
SUBST1_TAC(SYM(REAL_INT_REDUCE_CONV `&2 pow 2`)) THEN
MATCH_MP_TAC REAL_POW_MONO THEN
ASM_REWRITE_TAC[REAL_OF_NUM_LE; ARITH]];
ALL_TAC] THEN
SUBGOAL_THEN
`--(&1) pow p * s * x pow (SUC p) / &(SUC(SUC p)) -
&2 pow n * --(&1) pow (SUC p) * x pow (SUC(SUC p)) / &(SUC(SUC p)) =
(--(&1) pow p * x pow (SUC p) / &(SUC(SUC p))) *
(s - &2 pow n * --x)`
SUBST1_TAC THENL
[REWRITE_TAC[real_pow; real_div; GSYM REAL_OF_NUM_SUC] THEN
REWRITE_TAC[REAL_SUB_LDISTRIB; GSYM REAL_MUL_ASSOC] THEN
REWRITE_TAC[REAL_MUL_LNEG; REAL_MUL_RNEG; REAL_MUL_LID] THEN
REWRITE_TAC[REAL_NEG_NEG; REAL_MUL_AC]; ALL_TAC] THEN
ONCE_REWRITE_TAC[REAL_ABS_MUL] THEN
MATCH_MP_TAC REAL_LE_TRANS THEN
EXISTS_TAC `abs (-- (&1) pow p * x pow SUC p / &(SUC (SUC p))) * &1` THEN
ASM_SIMP_TAC[REAL_LE_LMUL; REAL_ABS_POS; REAL_LT_IMP_LE] THEN
REWRITE_TAC[REAL_MUL_RID; real_div; REAL_ABS_MUL; REAL_ABS_POW;
REAL_ABS_NEG; REAL_ABS_NUM; REAL_ABS_INV] THEN
REWRITE_TAC[REAL_POW_ONE; REAL_MUL_LID] THEN
MATCH_MP_TAC REAL_LE_TRANS THEN EXISTS_TAC `inv(&2) pow 1 * inv(&2)` THEN
CONJ_TAC THENL [ALL_TAC; CONV_TAC REAL_RAT_REDUCE_CONV] THEN
MATCH_MP_TAC REAL_LE_MUL2 THEN
SIMP_TAC[REAL_ABS_POS; REAL_POW_LE;
REAL_LE_INV_EQ; LE_0; REAL_OF_NUM_LE] THEN
CONJ_TAC THENL
[MATCH_MP_TAC REAL_LE_TRANS THEN EXISTS_TAC `inv(&2) pow (SUC p)` THEN
CONJ_TAC THENL
[MATCH_MP_TAC REAL_POW_LE2 THEN CONV_TAC REAL_RAT_REDUCE_CONV THEN
ASM_REWRITE_TAC[REAL_ABS_POS];
REWRITE_TAC[REAL_POW_INV] THEN MATCH_MP_TAC REAL_LE_INV2 THEN
CONJ_TAC THENL [CONV_TAC REAL_RAT_REDUCE_CONV; ALL_TAC] THEN
MATCH_MP_TAC REAL_POW_MONO THEN
REWRITE_TAC[REAL_OF_NUM_LE; ARITH] THEN ARITH_TAC];
MATCH_MP_TAC REAL_LE_INV2 THEN
REWRITE_TAC[REAL_OF_NUM_LT; ARITH; REAL_OF_NUM_LE] THEN ARITH_TAC]);;
(* ------------------------------------------------------------------------- *)
(* Special version of Taylor series for exponential in limited range. *)
(* ------------------------------------------------------------------------- *)
let MCLAURIN_EXP_LE1 = prove
(`!x n. abs(x) <= &1
==> ?t. abs(t) <= &1 /\
(exp(x) = sum(0,n) (\m. x pow m / &(FACT m)) +
(exp(t) / &(FACT n)) * x pow n)`,
REPEAT STRIP_TAC THEN
MP_TAC(SPECL [`x:real`; `n:num`] MCLAURIN_EXP_LE) THEN
DISCH_THEN(X_CHOOSE_THEN `t:real` STRIP_ASSUME_TAC) THEN
EXISTS_TAC `t:real` THEN ASM_REWRITE_TAC[] THEN
MATCH_MP_TAC REAL_LE_TRANS THEN EXISTS_TAC `abs(x)` THEN
ASM_REWRITE_TAC[]);;
let REAL_EXP_15 = prove
(`exp(&1) < &5`,
SUBST1_TAC(SYM(REAL_RAT_REDUCE_CONV `inv(&2) + inv(&2)`)) THEN
REWRITE_TAC[REAL_EXP_ADD] THEN
MATCH_MP_TAC REAL_LET_TRANS THEN
EXISTS_TAC `(&1 + &2 * inv(&2)) * (&1 + &2 * inv(&2))` THEN
CONV_TAC(RAND_CONV REAL_RAT_REDUCE_CONV) THEN
REWRITE_TAC[] THEN
MATCH_MP_TAC REAL_LE_MUL2 THEN
REWRITE_TAC[REAL_EXP_POS_LE] THEN
MATCH_MP_TAC REAL_EXP_BOUND_LEMMA THEN
CONV_TAC REAL_RAT_REDUCE_CONV);;
let TAYLOR_EXP_WEAK = prove
(`abs(x) <= &1 ==>
abs(exp(x) - sum(0,m) (\i. x pow i / &(FACT i))) < &5 * inv(&(FACT m))`,
DISCH_TAC THEN
FIRST_ASSUM(MP_TAC o SPEC `m:num` o MATCH_MP MCLAURIN_EXP_LE1) THEN
DISCH_THEN(X_CHOOSE_THEN `t:real` STRIP_ASSUME_TAC) THEN
ASM_REWRITE_TAC[REAL_ARITH `abs((x + y) - x) = abs(y)`] THEN
REWRITE_TAC[real_div; REAL_ABS_MUL; GSYM REAL_MUL_ASSOC] THEN
ASM_CASES_TAC `x = &0` THENL
[ASM_REWRITE_TAC[] THEN
SPEC_TAC(`m:num`,`m:num`) THEN INDUCT_TAC THENL
[REWRITE_TAC[real_pow; FACT; ABS_N; REAL_INV_1; REAL_MUL_RID] THEN
ASM_REWRITE_TAC[real_abs; REAL_EXP_POS_LE] THEN
MATCH_MP_TAC REAL_LET_TRANS THEN
EXISTS_TAC `exp(&1)` THEN REWRITE_TAC[REAL_EXP_15] THEN
REWRITE_TAC[REAL_EXP_MONO_LE] THEN
UNDISCH_TAC `abs(t) <= &1` THEN REAL_ARITH_TAC;
REWRITE_TAC[POW_0; REAL_ABS_0; REAL_MUL_RZERO] THEN
MATCH_MP_TAC REAL_LT_MUL THEN REWRITE_TAC[REAL_OF_NUM_LT; ARITH] THEN
MATCH_MP_TAC REAL_INV_POS THEN
REWRITE_TAC[REAL_OF_NUM_LT; FACT_LT]];
MATCH_MP_TAC REAL_LTE_TRANS THEN
EXISTS_TAC `&5 * abs(inv(&(FACT m))) * abs(x pow m)` THEN CONJ_TAC THENL
[MATCH_MP_TAC REAL_LT_RMUL_IMP THEN CONJ_TAC THENL
[MATCH_MP_TAC REAL_LET_TRANS THEN EXISTS_TAC `abs(exp(&1))` THEN
ASM_REWRITE_TAC[real_abs; REAL_EXP_POS_LE; REAL_EXP_MONO_LE;
REAL_EXP_15] THEN
UNDISCH_TAC `abs(t) <= &1` THEN REAL_ARITH_TAC;
MATCH_MP_TAC REAL_LT_MUL THEN
ASM_REWRITE_TAC[GSYM ABS_NZ; REAL_POW_EQ_0] THEN
REWRITE_TAC[REAL_INV_EQ_0; REAL_OF_NUM_EQ] THEN
MP_TAC(SPEC `m:num` FACT_LT) THEN ARITH_TAC];
MATCH_MP_TAC REAL_LE_LMUL_IMP THEN
REWRITE_TAC[REAL_OF_NUM_LE; ARITH] THEN
GEN_REWRITE_TAC RAND_CONV [GSYM REAL_MUL_RID] THEN
MATCH_MP_TAC REAL_LE_MUL2 THEN REWRITE_TAC[REAL_ABS_POS] THEN
REWRITE_TAC[REAL_ABS_INV; ABS_N; REAL_LE_REFL] THEN
REWRITE_TAC[REAL_ABS_POW] THEN
MATCH_MP_TAC REAL_POW_1_LE THEN
ASM_REWRITE_TAC[REAL_ABS_POS]]]);;
let REAL_EXP_13 = prove
(`exp(&1) < &3`,
MP_TAC(INST [`&1`,`x:real`; `5`,`m:num`] TAYLOR_EXP_WEAK) THEN
CONV_TAC(ONCE_DEPTH_CONV REAL_SUM_CONV) THEN
REWRITE_TAC[ADD_CLAUSES] THEN
CONV_TAC(ONCE_DEPTH_CONV NUM_FACT_CONV) THEN
CONV_TAC REAL_RAT_REDUCE_CONV THEN
MATCH_MP_TAC(REAL_ARITH
`b + e <= c ==> abs(a - b) < e ==> a < c`) THEN
CONV_TAC REAL_RAT_REDUCE_CONV);;
let TAYLOR_EXP = prove
(`abs(x) <= &1 ==>
abs(exp(x) - sum(0,m) (\i. x pow i / &(FACT i))) < &3 * inv(&(FACT m))`,
DISCH_TAC THEN
FIRST_ASSUM(MP_TAC o SPEC `m:num` o MATCH_MP MCLAURIN_EXP_LE1) THEN
DISCH_THEN(X_CHOOSE_THEN `t:real` STRIP_ASSUME_TAC) THEN
ASM_REWRITE_TAC[REAL_ARITH `abs((x + y) - x) = abs(y)`] THEN
REWRITE_TAC[real_div; REAL_ABS_MUL; GSYM REAL_MUL_ASSOC] THEN
ASM_CASES_TAC `x = &0` THENL
[ASM_REWRITE_TAC[] THEN
SPEC_TAC(`m:num`,`m:num`) THEN INDUCT_TAC THENL
[REWRITE_TAC[real_pow; FACT; ABS_N; REAL_INV_1; REAL_MUL_RID] THEN
ASM_REWRITE_TAC[real_abs; REAL_EXP_POS_LE] THEN
MATCH_MP_TAC REAL_LET_TRANS THEN
EXISTS_TAC `exp(&1)` THEN REWRITE_TAC[REAL_EXP_13] THEN
REWRITE_TAC[REAL_EXP_MONO_LE] THEN
UNDISCH_TAC `abs(t) <= &1` THEN REAL_ARITH_TAC;
REWRITE_TAC[POW_0; REAL_ABS_0; REAL_MUL_RZERO] THEN
MATCH_MP_TAC REAL_LT_MUL THEN REWRITE_TAC[REAL_OF_NUM_LT; ARITH] THEN
MATCH_MP_TAC REAL_INV_POS THEN
REWRITE_TAC[REAL_OF_NUM_LT; FACT_LT]];
MATCH_MP_TAC REAL_LTE_TRANS THEN
EXISTS_TAC `&3 * abs(inv(&(FACT m))) * abs(x pow m)` THEN CONJ_TAC THENL
[MATCH_MP_TAC REAL_LT_RMUL_IMP THEN CONJ_TAC THENL
[MATCH_MP_TAC REAL_LET_TRANS THEN EXISTS_TAC `abs(exp(&1))` THEN
ASM_REWRITE_TAC[real_abs; REAL_EXP_POS_LE; REAL_EXP_MONO_LE;
REAL_EXP_13] THEN
UNDISCH_TAC `abs(t) <= &1` THEN REAL_ARITH_TAC;
MATCH_MP_TAC REAL_LT_MUL THEN
ASM_REWRITE_TAC[GSYM ABS_NZ; REAL_POW_EQ_0] THEN
REWRITE_TAC[REAL_INV_EQ_0; REAL_OF_NUM_EQ] THEN
MP_TAC(SPEC `m:num` FACT_LT) THEN ARITH_TAC];
MATCH_MP_TAC REAL_LE_LMUL_IMP THEN
REWRITE_TAC[REAL_OF_NUM_LE; ARITH] THEN
GEN_REWRITE_TAC RAND_CONV [GSYM REAL_MUL_RID] THEN
MATCH_MP_TAC REAL_LE_MUL2 THEN REWRITE_TAC[REAL_ABS_POS] THEN
REWRITE_TAC[REAL_ABS_INV; ABS_N; REAL_LE_REFL] THEN
REWRITE_TAC[REAL_ABS_POW] THEN
MATCH_MP_TAC REAL_POW_1_LE THEN
ASM_REWRITE_TAC[REAL_ABS_POS]]]);;
let TAYLOR_LN = prove
(`&0 <= x /\ x <= inv(&2 pow k) ==>
abs(ln(&1 + x) - sum(0,m) (\i. --(&1) pow i * x pow SUC i / &(SUC i)))
< inv(&2 pow (k * SUC m) * &(SUC m))`,
let lemma = INST [`1`,`k:num`] (SYM(SPEC_ALL SUM_REINDEX)) in
STRIP_TAC THEN
UNDISCH_TAC `&0 <= x` THEN REWRITE_TAC[REAL_LE_LT] THEN
DISCH_THEN(DISJ_CASES_THEN2 ASSUME_TAC (SUBST1_TAC o SYM)) THENL
[ALL_TAC;
REWRITE_TAC[real_pow; REAL_MUL_LZERO; REAL_MUL_RZERO; real_div] THEN
REWRITE_TAC[SUM_0; REAL_ADD_RID; REAL_SUB_LZERO; LN_1] THEN
REWRITE_TAC[REAL_ABS_NEG; REAL_ABS_0] THEN
SIMP_TAC[REAL_LT_INV_EQ; REAL_LT_MUL; REAL_POW_LT; REAL_OF_NUM_LT;
LT_0; ARITH]] THEN
SUBGOAL_THEN `!i. --(&1) pow i = --(&1) pow (SUC(SUC i))`
(fun th -> ONCE_REWRITE_TAC[th]) THENL
[REWRITE_TAC[real_pow; REAL_MUL_LNEG; REAL_MUL_RNEG; REAL_NEG_NEG] THEN
REWRITE_TAC[REAL_MUL_LID]; ALL_TAC] THEN
REWRITE_TAC[ADD1; lemma] THEN
REWRITE_TAC[ADD_CLAUSES] THEN
ONCE_REWRITE_TAC[SUM_DIFF] THEN
CONV_TAC(ONCE_DEPTH_CONV REAL_SUM_CONV) THEN
REWRITE_TAC[real_div; REAL_INV_0; REAL_MUL_RZERO] THEN
REWRITE_TAC[GSYM ADD1] THEN
MP_TAC(SPECL [`x:real`; `SUC m`] MCLAURIN_LN_POS) THEN
ASM_REWRITE_TAC[LT_0] THEN
ONCE_REWRITE_TAC[ADD_SYM] THEN REWRITE_TAC[GSYM ADD1] THEN
REWRITE_TAC[GSYM real_div] THEN
DISCH_THEN(X_CHOOSE_THEN `t:real` STRIP_ASSUME_TAC) THEN
ASM_REWRITE_TAC[REAL_SUB_RZERO; REAL_ARITH `(a + b) - a = b`] THEN
REWRITE_TAC[real_div; REAL_ABS_MUL; REAL_ABS_INV; REAL_ABS_POW] THEN
REWRITE_TAC[REAL_ABS_NEG; REAL_ABS_NUM; REAL_POW_ONE] THEN
REWRITE_TAC[REAL_MUL_LID; REAL_INV_MUL; GSYM REAL_MUL_ASSOC] THEN
MATCH_MP_TAC REAL_LET_TRANS THEN EXISTS_TAC
`inv (&2 pow (k * SUC m)) * inv (&(SUC m)) * inv(abs(&1 + t) pow SUC m)` THEN
CONJ_TAC THENL
[REWRITE_TAC[GSYM REAL_MUL_ASSOC] THEN
MATCH_MP_TAC REAL_LE_RMUL THEN
SIMP_TAC[REAL_LE_MUL; REAL_LE_INV_EQ; REAL_POS; REAL_ABS_POS;
REAL_POW_LE] THEN
REWRITE_TAC[GSYM REAL_POW_INV] THEN
REWRITE_TAC[GSYM REAL_POW_POW] THEN
MATCH_MP_TAC REAL_POW_LE2 THEN
ASM_SIMP_TAC[REAL_POW_INV; real_abs; REAL_LT_IMP_LE];
GEN_REWRITE_TAC RAND_CONV [GSYM REAL_MUL_RID] THEN
REWRITE_TAC[REAL_MUL_ASSOC] THEN MATCH_MP_TAC REAL_LT_LMUL THEN
SIMP_TAC[REAL_LT_MUL; REAL_LT_INV_EQ; REAL_OF_NUM_LT; LT_0; REAL_POW_LT;
ARITH] THEN
REWRITE_TAC[GSYM REAL_POW_INV; GSYM REAL_ABS_INV] THEN
SUBGOAL_THEN `abs(inv(&1 + t)) < &1` ASSUME_TAC THENL
[REWRITE_TAC[REAL_ABS_INV] THEN
GEN_REWRITE_TAC RAND_CONV [GSYM REAL_INV_1] THEN
MATCH_MP_TAC REAL_LT_INV2 THEN
UNDISCH_TAC `&0 < t` THEN REAL_ARITH_TAC;
SUBST1_TAC(SYM(SPEC `SUC m` REAL_POW_ONE)) THEN
MATCH_MP_TAC REAL_POW_LT2 THEN
ASM_REWRITE_TAC[REAL_POW_ONE; NOT_SUC; REAL_ABS_POS]]]);;
(* ------------------------------------------------------------------------- *)
(* Leading from the summation to the actual function. *)
(* ------------------------------------------------------------------------- *)
let APPROX_LEMMA1 = prove
(`abs(f(x:real) - sum(0,m) (\i. P i x)) < inv(&2 pow (n + 2)) /\
abs(u - &2 pow (n + e + 2) * sum(0,m) (\i. P i x)) <= &k * &m /\
&k * &m <= &2 pow e /\
abs(s * &2 pow (e + 2) - u) <= &2 pow (e + 1)
==> abs(s - &2 pow n * f(x)) < &1`,
STRIP_TAC THEN MATCH_MP_TAC REAL_LT_LCANCEL_IMP THEN
EXISTS_TAC `&2 pow (n + e + 2)` THEN
REWRITE_TAC[REAL_LT_POW2] THEN
REWRITE_TAC[REAL_ABS_LEMMA; REAL_SUB_LDISTRIB; REAL_MUL_RID] THEN
ONCE_REWRITE_TAC[REAL_MUL_SYM] THEN (MATCH_MP_TAC o GEN_ALL)
(REAL_ARITH `abs(a - b) + abs(b - c) < d ==> abs(a - c) < d`) THEN
EXISTS_TAC `&2 pow n * u` THEN
CONV_TAC(funpow 4 RAND_CONV num_CONV) THEN
REWRITE_TAC[ADD_CLAUSES; real_pow; REAL_MUL_2] THEN
MATCH_MP_TAC REAL_LET_ADD2 THEN CONJ_TAC THENL
[ONCE_REWRITE_TAC[REAL_POW_ADD] THEN
GEN_REWRITE_TAC (LAND_CONV o RAND_CONV o LAND_CONV) [REAL_MUL_SYM] THEN
REWRITE_TAC[GSYM REAL_MUL_ASSOC; GSYM REAL_SUB_LDISTRIB] THEN
REWRITE_TAC[GSYM REAL_ABS_LEMMA] THEN
MATCH_MP_TAC REAL_LE_LMUL THEN
ONCE_REWRITE_TAC[REAL_MUL_SYM] THEN ASM_REWRITE_TAC[] THEN
MATCH_MP_TAC REAL_LT_IMP_LE THEN REWRITE_TAC[REAL_LT_POW2];
REWRITE_TAC[GSYM REAL_MUL_ASSOC; GSYM REAL_SUB_LDISTRIB] THEN
GEN_REWRITE_TAC RAND_CONV [REAL_POW_ADD] THEN
REWRITE_TAC[GSYM REAL_ABS_LEMMA] THEN
MATCH_MP_TAC REAL_LT_LMUL THEN REWRITE_TAC[REAL_LT_POW2] THEN
ONCE_REWRITE_TAC[REAL_MUL_SYM] THEN (MATCH_MP_TAC o GEN_ALL)
(REAL_ARITH `abs(a - b) + abs(b - c) < d ==> abs(a - c) < d`) THEN
EXISTS_TAC
`&2 pow (n + e + 2) * sum(0,m) (\i. P i (x:real))` THEN
GEN_REWRITE_TAC RAND_CONV [REAL_POW_ADD] THEN
GEN_REWRITE_TAC RAND_CONV [REAL_MUL_SYM] THEN
REWRITE_TAC[REAL_POW_1; REAL_MUL_2] THEN
MATCH_MP_TAC REAL_LET_ADD2 THEN CONJ_TAC THENL
[MATCH_MP_TAC REAL_LE_TRANS THEN EXISTS_TAC `&k * &m` THEN
ASM_REWRITE_TAC[];
REWRITE_TAC[GSYM REAL_SUB_LDISTRIB; GSYM REAL_ABS_LEMMA] THEN
ONCE_REWRITE_TAC[ADD_SYM] THEN REWRITE_TAC[GSYM ADD_ASSOC] THEN
ONCE_REWRITE_TAC[REAL_POW_ADD] THEN
REWRITE_TAC[GSYM REAL_MUL_ASSOC] THEN
GEN_REWRITE_TAC RAND_CONV [GSYM REAL_MUL_RID] THEN
MATCH_MP_TAC REAL_LT_LMUL THEN
REWRITE_TAC[REAL_LT_POW2] THEN ONCE_REWRITE_TAC[ADD_SYM] THEN
MATCH_MP_TAC REAL_LT_LCANCEL_IMP THEN
EXISTS_TAC `inv(&2 pow (n + 2))` THEN
REWRITE_TAC[REAL_LT_INV_EQ; REAL_LT_POW2] THEN
REWRITE_TAC[REAL_MUL_RID; REAL_MUL_ASSOC] THEN
ONCE_REWRITE_TAC[REAL_ABS_SUB] THEN
SUBGOAL_THEN `inv(&2 pow (n + 2)) * &2 pow (n + 2) = &1`
(fun th -> ASM_REWRITE_TAC[th; REAL_MUL_LID]) THEN
MATCH_MP_TAC REAL_MUL_LINV THEN REWRITE_TAC[REAL_POW_EQ_0] THEN
REWRITE_TAC[DE_MORGAN_THM] THEN DISJ1_TAC THEN REAL_ARITH_TAC]]);;
(* ------------------------------------------------------------------------- *)
(* Approximation theorems. *)
(* ------------------------------------------------------------------------- *)
let APPROX_EXP = prove
(`(n + e + 2 = p) /\
&3 * &2 pow (n + 2) <= &(FACT m) /\
&2 * &m <= &2 pow e /\
abs(x) <= &1 /\
abs(s - &2 pow p * x) < &1 /\
(t(0) = &2 pow p) /\
(!k. SUC k < m ==>
&2 * abs(t(SUC k) * &2 pow p * &(SUC k) - s * t(k))
<= &2 pow p * &(SUC k)) /\
abs(u * &2 pow (e + 2) - sum(0,m) t) <= &2 pow (e + 1)
==> abs(u - &2 pow n * exp(x)) < &1`,
STRIP_TAC THEN MATCH_MP_TAC(GEN_ALL APPROX_LEMMA1) THEN
MAP_EVERY EXISTS_TAC
[`\i x. x pow i / &(FACT i)`; `2`; `m:num`; `sum(0,m) t`; `e:num`] THEN
ASM_REWRITE_TAC[BETA_THM] THEN CONJ_TAC THENL
[MATCH_MP_TAC REAL_LTE_TRANS THEN EXISTS_TAC `&3 * inv(&(FACT m))` THEN
CONJ_TAC THENL
[MATCH_MP_TAC TAYLOR_EXP THEN ASM_REWRITE_TAC[];
SUBST1_TAC(SYM(SPEC `&3` REAL_INV_INV)) THEN
REWRITE_TAC[GSYM REAL_INV_MUL] THEN
MATCH_MP_TAC REAL_LE_INV2 THEN ASM_REWRITE_TAC[REAL_LT_POW2] THEN
MATCH_MP_TAC REAL_LE_LCANCEL_IMP THEN EXISTS_TAC `&3` THEN
REWRITE_TAC[REAL_MUL_ASSOC] THEN
REWRITE_TAC[MATCH_MP REAL_MUL_RINV (REAL_ARITH `~(&3 = &0)`)] THEN
ASM_REWRITE_TAC[REAL_MUL_LID] THEN REAL_ARITH_TAC];
MATCH_MP_TAC STEPS_EXP THEN ASM_REWRITE_TAC[]]);;
let APPROX_LN = prove
(`~(k = 0) /\
(n + e + 2 = p) /\
&2 pow (n + 2) <= &2 pow (k * SUC m) * &(SUC m) /\
&3 * &m <= &2 pow e /\
(&0 <= x /\ x <= inv(&2 pow k)) /\
abs(s - &2 pow p * --x) < &1 /\
(t(0) = --s) /\
(!k. SUC k < m ==>
&2 * abs(t(SUC k) * &2 pow p * &(SUC(SUC k)) -
&(SUC k) * s * t(k))
<= &2 pow p * &(SUC(SUC k))) /\
abs(u * &2 pow (e + 2) - sum(0,m) t) <= &2 pow (e + 1)
==> abs(u - &2 pow n * ln(&1 + x)) < &1`,
STRIP_TAC THEN
(MATCH_MP_TAC o GEN_ALL o BETA_RULE)
(INST [`\x. ln(&1 + x):real`,`f:real->real`] APPROX_LEMMA1) THEN
MAP_EVERY EXISTS_TAC
[`\i x. (--(&1)) pow i * x pow (SUC i) / &(SUC i)`;
`3`; `m:num`; `sum(0,m) t`; `e:num`] THEN
ASM_REWRITE_TAC[BETA_THM] THEN CONJ_TAC THENL
[MATCH_MP_TAC REAL_LTE_TRANS THEN
EXISTS_TAC `inv(&2 pow (k * SUC m) * &(SUC m))` THEN CONJ_TAC THENL
[MATCH_MP_TAC TAYLOR_LN THEN ASM_REWRITE_TAC[];
MATCH_MP_TAC REAL_LE_INV2 THEN ASM_REWRITE_TAC[REAL_LT_POW2]];
MATCH_MP_TAC STEPS_LN THEN ASM_REWRITE_TAC[] THEN
SUBGOAL_THEN `2 <= (n + e + 2)` MP_TAC THENL
[REWRITE_TAC[ADD_ASSOC] THEN ONCE_REWRITE_TAC[ADD_SYM] THEN
REWRITE_TAC[LE_ADD];
SUBGOAL_THEN `abs(x) <= &1 / &2` (fun th -> ASM_REWRITE_TAC[th]) THEN
ASM_REWRITE_TAC[real_abs] THEN MATCH_MP_TAC REAL_LE_TRANS THEN
EXISTS_TAC `inv(&2 pow k)` THEN ASM_REWRITE_TAC[] THEN
REWRITE_TAC[real_div; REAL_MUL_LID] THEN
GEN_REWRITE_TAC (RAND_CONV o RAND_CONV) [GSYM REAL_POW_1] THEN
MATCH_MP_TAC REAL_LE_INV2 THEN REWRITE_TAC[REAL_LT_POW2] THEN
MATCH_MP_TAC REAL_POW_MONO THEN
REWRITE_TAC[REAL_OF_NUM_LE; ARITH] THEN
UNDISCH_TAC `~(k = 0)` THEN ARITH_TAC]]);;
(* ------------------------------------------------------------------------- *)
(* Eliminate trivial definitions. *)
(* ------------------------------------------------------------------------- *)
let ELIMINATE_DEF =
let x_tm = `x:num`
and a_tm = `&0`
and sconv = REWRITE_CONV[ARITH] in
fun tdefs th ->
if tdefs = [] then th else
let ctm =
itlist (fun tm acc ->
let l,r = (rand F_F I) (dest_eq tm) in
mk_cond(mk_eq(x_tm,l),r,acc)) tdefs a_tm in
let atm = mk_abs(x_tm,ctm) in
let ttm = rator(lhs(hd tdefs)) in
let tth = ASSUME(mk_eq(ttm,atm)) in
let ths = map
(EQT_ELIM o CONV_RULE(RAND_CONV sconv) o SUBS_CONV[tth]) tdefs in
let dth = PROVE_HYP (end_itlist CONJ ths) th in
MP (INST [atm,ttm] (DISCH_ALL dth)) (REFL atm);;
(* ------------------------------------------------------------------------- *)
(* Overall conversion. *)
(* ------------------------------------------------------------------------- *)
let realcalc_cache = ref [];;
let REALCALC_CONV,thm_eval,raw_eval,thm_wrap =
let a_tm = `a:real` and n_tm = `n:num` and n'_tm = `n':num`
and m_tm = `m:num`
and b_tm = `b:real` and e_tm = `e:num`
and c_tm = `c:real`
and neg_tm = `(--)`
and abs_tm = `abs`
and inv_tm = `inv`
and sqrt_tm = `sqrt`
and add_tm = `(+)`
and mul_tm = `(*)`
and sub_tm = `(-)`
and exp_tm = `exp:real->real`
and ln_tm = `ln:real->real`
and add1_tm = `(+) (&1)`
and pow2_tm = `(pow) (&2)`
and one_tm = `&1`
and lt_tm = `(<)` in
let INTEGER_PROVE =
EQT_ELIM o REWRITE_CONV[REAL_EQ_NEG2; GSYM EXISTS_REFL;
EXISTS_OR_THM; REAL_OF_NUM_EQ] in
let ndiv x y =
let q = quo_num x y in
let r = x -/ (q */ y) in
if le_num (abs_num(Int 2 */ r)) (abs_num y) then q
else if le_num (abs_num(Int 2 */ (r -/ y))) (abs_num y) then q +/ Int 1
else if le_num (abs_num(Int 2 */ (r +/ y))) (abs_num y) then q -/ Int 1
else let s = (string_of_num x)^" and "^(string_of_num y) in
failwith ("ndiv: "^s) in
let raw_wrap (f:num->num) = (ref(Int(-1),Int 0),f) in
let raw_eval(r,(f:num->num)) n =
let (n0,y0) = !r in
if le_num n n0 then ndiv y0 (power_num (Int 2) (n0 -/ n))
else let y = f n in (r := (n,y); y) in
let thm_eval =
let SUC_tm = `SUC`
and mk_add = mk_binop `(+):num->num->num` in
fun (r,(f:num->thm)) n ->
let (n0,y0th) = !r in
if le_num n n0 then
if n =/ n0 then y0th else
let th1 = NUM_SUC_CONV
(mk_comb(SUC_tm,mk_numeral(n0 -/ (n +/ Int 1)))) in
let th2 = MATCH_MP REALCALC_DOWNGRADE th1 in
let th3 = NUM_ADD_CONV(mk_add(mk_numeral(n)) (mk_numeral(n0 -/ n))) in
let th4 = MATCH_MP th2 th3 in
let th5 = MATCH_MP th4 y0th in
let tm5 = fst(dest_imp(concl th5)) in
let tm5a,tm5b = dest_comb tm5 in
let th6 = REAL_INT_POW_CONV tm5b in
let tm5c = rand(rand tm5a) in
let tm5d,tm5e = dest_comb tm5c in
let tm5f,tm5g = dest_comb(rand tm5d) in
let tm5h = rand(rand tm5f) in
let bin = mk_realintconst
(ndiv (dest_realintconst tm5e) (power_num (Int 2) (dest_numeral tm5h))) in
let th7 = AP_TERM (rator(rand tm5f)) th1 in
let th8 = GEN_REWRITE_RULE LAND_CONV [CONJUNCT2 real_pow] th7 in
let th9 = SYM(GEN_REWRITE_RULE (LAND_CONV o RAND_CONV) [th6] th8) in
let th10 = TRANS th9 (REAL_INT_MUL_CONV (rand(concl th9))) in
let th11 = AP_THM (AP_TERM (rator tm5f) th10) bin in
let th12 = TRANS th11 (REAL_INT_MUL_CONV (rand(concl th11))) in
let th13 = AP_THM (AP_TERM (rator tm5d) th12) tm5e in
let th14 = TRANS th13 (REAL_INT_SUB_CONV (rand(concl th13))) in
let th15 = AP_TERM (rator(rand tm5a)) th14 in
let th16 = TRANS th15 (REAL_INT_ABS_CONV (rand(concl th15))) in
let th17 = MK_COMB(AP_TERM (rator tm5a) th16,th6) in
let th18 = TRANS th17 (REAL_INT_LE_CONV (rand(concl th17))) in
MATCH_MP th5 (EQT_ELIM th18)
else let yth = f n in (r := (n,yth); yth) in
let thm_wrap (f:num->thm) = (ref(Int(-1),TRUTH),f) in
let find_msd =
let rec find_msd n f =
if Int 1 </ abs_num(raw_eval f n) then n
else find_msd (n +/ Int 1) f in
find_msd (Int 0) in
let find_acc =
let rec find_msd n f =
if Int 32 </ abs_num(raw_eval f n) then n
else find_msd (n +/ Int 1) f in
find_msd (Int 0) in
let find_ubound f =
let k = find_acc f in
let a = abs_num(raw_eval f k) in
k -/ log2 (a +/ Int 1) in
let REALCALC_EXP_CONV =
let t_tm = `t:num->real`
and n_tm = `n:num`
and m_tm = `m:num`
and e_tm = `e:num`
and p_tm = `p:num`
and s_tm = `s:real`
and u_tm = `u:real`
and x_tm = `x:real` in
let rec calculate_m acc i r =
if acc >=/ r then i else
let i' = i +/ Int 1 in
calculate_m (i' */ acc) i' r in
let calculate_exp_sequence =
let rec calculate_exp_sequence p2 s i =
if i </ Int 0 then []
else if i =/ Int 0 then [p2] else
let acc = calculate_exp_sequence p2 s (i -/ Int 1) in
let t = hd acc in
let t' = ndiv (s */ t) (p2 */ i) in
t'::acc in
fun p s m -> let p2 = power_num (Int 2) p in
rev(calculate_exp_sequence p2 s (m -/ Int 1)) in
let pth = prove
(`abs(x) <= &1 ==>
abs(s - &2 pow p * x) < &1 ==>
(n + e + 2 = p) /\
&3 * &2 pow (n + 2) <= &(FACT m) /\
&2 * &m <= &2 pow e /\
(t(0) = &2 pow p) /\
(!k. SUC k < m ==>
&2 * abs(t(SUC k) * &2 pow p * &(SUC k) - s * t(k))
<= &2 pow p * &(SUC k)) /\
abs(u * &2 pow (e + 2) - sum(0,m) t) <= &2 pow (e + 1)
==> abs(u - &2 pow n * exp(x)) < &1`,
REPEAT STRIP_TAC THEN MATCH_MP_TAC APPROX_EXP THEN
ASM_REWRITE_TAC[]) in
let LEFT_ZERO_RULE =
ONCE_REWRITE_RULE[prove(`0 + n = n`,REWRITE_TAC[ADD_CLAUSES])] in
fun (fn1,fn2) ->
let raw_fn n =
let m = calculate_m (Int 1) (Int 0)
(Int 3 */ (power_num (Int 2) (n +/ Int 2))) in
let e = log2 (Int 2 */ m) in
let p = n +/ e +/ Int 2 in
let s = raw_eval fn1 p in
let seq = calculate_exp_sequence p s m in
let u0 = itlist (+/) seq (Int 0) in
ndiv u0 (power_num (Int 2) (e +/ Int 2))
and thm_fn n =
let m = calculate_m (Int 1) (Int 0)
(Int 3 */ (power_num (Int 2) (n +/ Int 2))) in
let e = log2 (Int 2 */ m) in
let p = n +/ e +/ Int 2 in
let sth = thm_eval fn2 p in
let tm1 = rand(lhand(concl sth)) in
let s_num = lhand tm1 in
let x_num = rand(rand tm1) in
let s = dest_realintconst s_num in
let seq = calculate_exp_sequence p s m in
let u0 = itlist (+/) seq (Int 0) in
let u = ndiv u0 (power_num (Int 2) (e +/ Int 2)) in
let m_num = mk_numeral m
and n_num = mk_numeral n
and e_num = mk_numeral e
and p_num = mk_numeral p
and u_num = mk_realintconst u in
let tdefs = map2 (fun a b -> mk_eq(mk_comb(t_tm,mk_small_numeral a),
mk_realintconst b)) (0--(length seq - 1)) seq in
let p2th = REAL_INT_POW_CONV (mk_comb(pow2_tm,p_num)) in
let th0 = INST [m_num,m_tm; n_num,n_tm; e_num,e_tm;
x_num,x_tm; p_num,p_tm; s_num,s_tm; u_num,u_tm] pth in
let th0' = MP th0 (EQT_ELIM(REAL_RAT_REDUCE_CONV(lhand(concl th0)))) in
let th1 = MP th0' sth in
let th2 = CONV_RULE (ONCE_DEPTH_CONV EXPAND_RANGE_CONV) th1 in
let th3 = LEFT_ZERO_RULE
(CONV_RULE (ONCE_DEPTH_CONV REAL_SUM_CONV) th2) in
let ths = try CONJUNCTS(ASSUME(list_mk_conj tdefs))
with Failure _ -> [] in
let th4 = SUBS (p2th::ths) th3 in
let th5 = CONV_RULE (LAND_CONV
(DEPTH_CONV NUM_ADD_CONV THENC
ONCE_DEPTH_CONV NUM_FACT_CONV THENC
REAL_INT_REDUCE_CONV)) th4 in
MP (ELIMINATE_DEF tdefs th5) TRUTH in
raw_wrap raw_fn,thm_wrap thm_fn in
let REALCALC_LN_CONV =
let t_tm = `t:num->real`
and n_tm = `n:num`
and m_tm = `m:num`
and e_tm = `e:num`
and p_tm = `p:num`
and s_tm = `s:real`
and u_tm = `u:real`
and k_tm = `k:num`
and x_tm = `x:real` in
let rec calculate_m acc k2 m r =
if acc */ (m +/ Int 1) >=/ r then m else
calculate_m (k2 */ acc) k2 (m +/ Int 1) r in
let calculate_ln_sequence =
let rec calculate_ln_sequence p2 s i =
if i </ Int 0 then []
else if i =/ Int 0 then [s] else
let acc = calculate_ln_sequence p2 s (i -/ Int 1) in
let t = hd acc in
let t' = ndiv (Int(-1) */ s */ t */ i) (p2 */ (i +/ Int 1)) in
t'::acc in
fun p s m -> let p2 = power_num (Int 2) p in
rev(calculate_ln_sequence p2 s (m -/ Int 1)) in
let pth = prove
(`&0 <= x /\ x <= inv(&2 pow k) ==>
abs(s - &2 pow p * x) < &1 ==>
~(k = 0) /\
(n + e + 2 = p) /\
&2 pow (n + 2) <= &2 pow (k * SUC m) * &(SUC m) /\
&3 * &m <= &2 pow e /\
(t(0) = s) /\
(!k. SUC k < m ==>
&2 * abs(t(SUC k) * &2 pow p * &(SUC(SUC k)) -
&(SUC k) * --s * t(k))
<= &2 pow p * &(SUC(SUC k))) /\
abs(u * &2 pow (e + 2) - sum(0,m) t) <= &2 pow (e + 1)
==> abs(u - &2 pow n * ln(&1 + x)) < &1`,
REPEAT STRIP_TAC THEN MATCH_MP_TAC(INST [`--s`,`s:real`] APPROX_LN) THEN
ASM_REWRITE_TAC[REAL_NEG_NEG] THEN
REWRITE_TAC[REAL_MUL_RNEG] THEN
REWRITE_TAC[REAL_ARITH `abs(--a - --b) = abs(a - b)`] THEN
ASM_REWRITE_TAC[]) in
let LEFT_ZERO_RULE =
ONCE_REWRITE_RULE[prove(`0 + n = n`,REWRITE_TAC[ADD_CLAUSES])] in
let pow2_tm = `(pow) (&2)` in
let default_tdefs = [`t 0 = &0`] in
fun (fn1,fn2) ->
let raw_fn n =
let k = find_ubound fn1 in
if k </ Int 1 then failwith "ln of number not provably <= 1/2" else
let k2 = power_num (Int 2) k in
let m = calculate_m k2 k2 (Int 0) (power_num (Int 2) (n +/ Int 2)) in
let e = log2 (Int 3 */ m) in
let p = n +/ e +/ Int 2 in
let s = raw_eval fn1 p in
let seq = calculate_ln_sequence p s m in
let u0 = itlist (+/) seq (Int 0) in
ndiv u0 (power_num (Int 2) (e +/ Int 2))
and thm_fn n =
let k = find_ubound fn1 in
if k </ Int 1 then failwith "ln of number not provably <= 1/2" else
let k2 = power_num (Int 2) k in
let m = calculate_m k2 k2 (Int 0) (power_num (Int 2) (n +/ Int 2)) in
let e = log2 (Int 3 */ m) in
let p = n +/ e +/ Int 2 in
let sth = thm_eval fn2 p in
let tm1 = rand(lhand(concl sth)) in
let s_num = lhand tm1 in
let x_num = rand(rand tm1) in
let s = dest_realintconst s_num in
let seq = calculate_ln_sequence p s m in
let u0 = itlist (+/) seq (Int 0) in
let u = ndiv u0 (power_num (Int 2) (e +/ Int 2)) in
let m_num = mk_numeral m
and n_num = mk_numeral n
and e_num = mk_numeral e
and p_num = mk_numeral p
and k_num = mk_numeral k
and u_num = mk_realintconst u in
let tdefs0 = map2 (fun a b -> mk_eq(mk_comb(t_tm,mk_small_numeral a),
mk_realintconst b)) (0--(length seq - 1)) seq in
let tdefs = if tdefs0 = [] then default_tdefs else tdefs0 in
let p2th = REAL_INT_POW_CONV (mk_comb(pow2_tm,p_num)) in
let th0 = INST [m_num,m_tm; n_num,n_tm; e_num,e_tm; k_num,k_tm;
x_num,x_tm; p_num,p_tm; s_num,s_tm; u_num,u_tm] pth in
let th0' = MP th0 (EQT_ELIM(REAL_RAT_REDUCE_CONV(lhand(concl th0)))) in
let th1 = MP th0' sth in
let th2 = CONV_RULE (ONCE_DEPTH_CONV EXPAND_RANGE_CONV) th1 in
let th3 = LEFT_ZERO_RULE
(CONV_RULE (ONCE_DEPTH_CONV REAL_SUM_CONV) th2) in
let ths = try CONJUNCTS(ASSUME(list_mk_conj tdefs))
with Failure _ -> [] in
let th4 = SUBS (p2th::ths) th3 in
let th5 = CONV_RULE (LAND_CONV
(NUM_REDUCE_CONV THENC
REAL_INT_REDUCE_CONV)) th4 in
MP (ELIMINATE_DEF tdefs th5) TRUTH in
raw_wrap raw_fn,thm_wrap thm_fn in
let REALCALC_SQRT_CONV =
let num_sqrt =
let rec isolate_sqrt (a,b) y =
if abs_num(a -/ b) <=/ Int 1 then
if abs_num(a */ a -/ y) <=/ a then a else b
else
let c = quo_num (a +/ b) (Int 2) in
if c */ c <=/ y then isolate_sqrt (c,b) y
else isolate_sqrt (a,c) y in
fun n -> isolate_sqrt (Int 0,n) n in
let MATCH_pth = MATCH_MP REALCALC_SQRT in
let b_tm = `b:real` in
let PROVE_1_LE_SQRT =
let pth = prove
(`&1 <= x ==> &1 <= sqrt(x)`,
DISCH_THEN(fun th ->
ASSUME_TAC(MATCH_MP (REAL_ARITH `&1 <= x ==> &0 <= x`) th) THEN
MP_TAC th) THEN
CONV_TAC CONTRAPOS_CONV THEN REWRITE_TAC[REAL_NOT_LE] THEN
DISCH_TAC THEN
SUBGOAL_THEN `x = sqrt(x) pow 2` SUBST1_TAC THENL
[CONV_TAC SYM_CONV THEN ASM_REWRITE_TAC[SQRT_POW2];
GEN_REWRITE_TAC RAND_CONV [GSYM REAL_MUL_LID] THEN
REWRITE_TAC[POW_2] THEN MATCH_MP_TAC REAL_LT_MUL2 THEN
ASM_SIMP_TAC[SQRT_POS_LE]]) in
let tac = REPEAT(MATCH_MP_TAC pth) THEN CONV_TAC REAL_RAT_LE_CONV in
fun tm -> try prove(tm,tac)
with Failure _ -> failwith "Need root body >= &1" in
fun (fn1,fn2) ->
let raw_fn n =
num_sqrt(power_num (Int 2) n */ raw_eval fn1 n)
and thm_fn n =
let th1 = MATCH_pth(thm_eval fn2 n) in
let th2 = MP th1 (PROVE_1_LE_SQRT(lhand(concl th1))) in
let th3 = CONV_RULE(funpow 2 LAND_CONV
(funpow 2 RAND_CONV REAL_RAT_REDUCE_CONV)) th2 in
let k = dest_realintconst(rand(rand(lhand(lhand(concl th3))))) in
let th4 = INST [mk_realintconst(num_sqrt k),b_tm] th3 in
MP th4 (EQT_ELIM(REAL_RAT_REDUCE_CONV(lhand(concl th4)))) in
raw_wrap raw_fn,thm_wrap thm_fn in
let rec REALCALC_CONV tm =
try assoc tm (!realcalc_cache) with Failure _ ->
if is_ratconst tm then
let x = rat_of_term tm in
let raw_fn acc =
floor_num ((power_num (Int 2) acc) */ x)
and thm_fn acc =
let a = floor_num ((power_num (Int 2) acc) */ x) in
let atm = mk_realintconst a in
let rtm = mk_comb(mk_comb(mul_tm,mk_comb(pow2_tm,mk_numeral acc)),tm) in
let btm = mk_comb(abs_tm,mk_comb(mk_comb(sub_tm,atm),rtm)) in
let ftm = mk_comb(mk_comb(lt_tm,btm),one_tm) in
EQT_ELIM(REAL_RAT_REDUCE_CONV ftm) in
raw_wrap raw_fn,thm_wrap thm_fn else
let lop,r = dest_comb tm in
if lop = neg_tm then
let rfn,tfn = REALCALC_CONV r in
let raw_fn acc =
minus_num (raw_eval rfn acc)
and thm_fn acc =
let th1 = thm_eval tfn acc in
let th2 = MATCH_MP REALCALC_NEG th1 in
try EQ_MP (LAND_CONV(RAND_CONV(LAND_CONV REAL_INT_NEG_CONV)) (concl th2))
th2
with Failure _ -> th2 in
raw_wrap raw_fn,thm_wrap thm_fn
else if lop = abs_tm then
let rfn,tfn = REALCALC_CONV r in
let raw_fn acc =
abs_num (raw_eval rfn acc)
and thm_fn acc =
let th1 = thm_eval tfn acc in
let th2 = MATCH_MP REALCALC_ABS th1 in
CONV_RULE (LAND_CONV(RAND_CONV(LAND_CONV REAL_INT_ABS_CONV))) th2 in
raw_wrap raw_fn,thm_wrap thm_fn
else if lop = sqrt_tm then
REALCALC_SQRT_CONV(REALCALC_CONV r)
else if lop = inv_tm then
let rfn,tfn = REALCALC_CONV r in
let x0 = raw_eval rfn (Int 0) in
let ax0 = abs_num x0 in
let r = log2(ax0) -/ Int 1 in
let get_ek(acc) =
if r < Int 0 then
let p = find_msd rfn in
let e = acc +/ p +/ Int 1 in
let k = e +/ p in e,k
else
let k = let k0 = acc +/ Int 1 -/ (Int 2 */ r) in
if k0 </ Int 0 then Int 0 else k0 in
let e = r +/ k in e,k in
let raw_fn acc =
let _,k = get_ek(acc) in
let nk2 = power_num (Int 2) (acc +/ k) in
ndiv nk2 (raw_eval rfn k) in
let thm_fn acc =
let e,k = get_ek(acc) in
let nk2 = power_num (Int 2) (acc +/ k) in
let th1 = thm_eval tfn k in
let atm = lhand(rand(lhand(concl th1))) in
let a = dest_realintconst atm in
let b = ndiv nk2 a in
let btm = mk_realintconst b in
let etm = mk_numeral e in
let ntm = mk_numeral acc in
let th2 = MATCH_MP REALCALC_INV th1 in
let th3 = INST [btm,b_tm; etm,e_tm; ntm,n_tm] th2 in
let th4 = MP th3 (INTEGER_PROVE(lhand(concl th3))) in
let th5 = MP th4 (INTEGER_PROVE(lhand(concl th4))) in
let th6 = MP th5 (EQT_ELIM(NUM_REDUCE_CONV(lhand(concl th5)))) in
let th7 = MP th6 (EQT_ELIM(REAL_INT_REDUCE_CONV(lhand(concl th6)))) in
MP th7
(EQT_ELIM(((LAND_CONV (funpow 4 RAND_CONV NUM_ADD_CONV) THENC
REAL_INT_REDUCE_CONV) (lhand(concl th7))))) in
raw_wrap raw_fn,thm_wrap thm_fn
else if lop = exp_tm then
let rfn,tfn = REALCALC_CONV r in
REALCALC_EXP_CONV (rfn,tfn)
else if lop = ln_tm then
let r1,r2 = dest_comb r in
if r1 = add1_tm then
let rfn,tfn = REALCALC_CONV r2 in
REALCALC_LN_CONV (rfn,tfn)
else
failwith "Can only do logs like ln(&1 + x) for small rational x" else
let op,l = dest_comb lop in
if op = add_tm then
let rfn1,tfn1 = REALCALC_CONV l
and rfn2,tfn2 = REALCALC_CONV r in
let raw_fn acc =
let acc' = acc +/ Int 2 in
ndiv (raw_eval rfn1 acc' +/ raw_eval rfn2 acc') (Int 4)
and thm_fn acc =
let acc' = acc +/ Int 2 in
let th1 = INST [mk_numeral acc,n_tm] REALCALC_ADD in
let th2 = MATCH_MP th1 (NUM_ADD_CONV (lhand(lhand(concl th1)))) in
let th3 = thm_eval tfn1 acc' in
let th4 = MATCH_MP th2 th3 in
let th5 = thm_eval tfn2 acc' in
let th6 = MATCH_MP th4 th5 in
let n1 = dest_realintconst(lhand(rand(lhand(concl th3))))
and n2 = dest_realintconst(lhand(rand(lhand(concl th5)))) in
let ci = mk_realintconst(ndiv (n1 +/ n2) (Int 4)) in
let th7 = INST [ci,c_tm] th6 in
let th8 = EQT_ELIM(REAL_INT_REDUCE_CONV(lhand(concl th7))) in
MP th7 th8 in
raw_wrap raw_fn,thm_wrap thm_fn
else if op = mul_tm then
let rfn1,tfn1 = REALCALC_CONV l
and rfn2,tfn2 = REALCALC_CONV r in
let get_kl(acc) =
let n' = acc +/ Int 2 in
let r = quo_num n' (Int 2) in
let s = n' -/ r in
let p = log2(abs_num(raw_eval rfn1 r))
and q = log2(abs_num(raw_eval rfn2 s)) in
let k = q +/ r +/ Int 1
and l = p +/ s +/ Int 1 in
if p =/ Int 0 && q = Int 0 then
if k </ l then k +/ Int 1,l else k,l +/ Int 1
else k,l in
let raw_fn acc =
let k,l = get_kl acc in
let m = (k +/ l) -/ acc in
ndiv (raw_eval rfn1 k */ raw_eval rfn2 l) (power_num (Int 2) m) in
let thm_fn acc =
let k,l = get_kl acc in
let m = (k +/ l) -/ acc in
let th1a = thm_eval tfn1 k
and th1b = thm_eval tfn2 l in
let a = dest_realintconst(lhand(rand(lhand(concl th1a))))
and b = dest_realintconst(lhand(rand(lhand(concl th1b)))) in
let c = ndiv (a */ b) (power_num (Int 2) m) in
let ntm = mk_numeral acc
and mtm = mk_numeral m
and ctm = mk_realintconst c in
let th1 = MATCH_MP REALCALC_MUL th1a in
let th2 = MATCH_MP th1 th1b in
let th3 = INST [ntm,n_tm; mtm,m_tm; ctm,c_tm] th2 in
let th4 = MP th3 (EQT_ELIM(NUM_REDUCE_CONV(lhand(concl th3)))) in
let th5 = MP th4 (EQT_ELIM(REAL_INT_REDUCE_CONV(lhand(concl th4)))) in
MP th5 (EQT_ELIM(REAL_INT_REDUCE_CONV(lhand(concl th5)))) in
raw_wrap raw_fn,thm_wrap thm_fn
else failwith "No other operators work yet, sorry!" in
REALCALC_CONV,thm_eval,raw_eval,thm_wrap;;
(* ------------------------------------------------------------------------- *)
(* Apply some conversion before doing approximation. *)
(* ------------------------------------------------------------------------- *)
let REALCALC_PRECONV conv tm =
let th = conv tm in
let rfn,tfn = REALCALC_CONV (rand(concl th)) in
rfn,
thm_wrap(fun n ->
let th1 = thm_eval tfn n in
GEN_REWRITE_RULE (LAND_CONV o funpow 3 RAND_CONV) [SYM th] th1);;
(* ------------------------------------------------------------------------- *)
(* Calculate ordering relation between two expressions. *)
(* ------------------------------------------------------------------------- *)
let REALCALC_LT = prove
(`abs(a - &2 pow n * x) < &1 /\ abs(b - &2 pow n * y) < &1
==> &2 <= abs(a - b) ==> (x < y <=> a < b)`,
REPEAT STRIP_TAC THEN MATCH_MP_TAC EQ_TRANS THEN
EXISTS_TAC `&2 pow n * x < &2 pow n * y` THEN CONJ_TAC THENL
[SIMP_TAC[REAL_LT_LMUL_EQ; REAL_POW_LT; REAL_OF_NUM_LT; ARITH];
POP_ASSUM_LIST(MP_TAC o end_itlist CONJ) THEN REAL_ARITH_TAC]);;
let REALCALC_LE = prove
(`abs(a - &2 pow n * x) < &1 /\ abs(b - &2 pow n * y) < &1
==> &2 <= abs(a - b) ==> (x <= y <=> a <= b)`,
REPEAT STRIP_TAC THEN MATCH_MP_TAC EQ_TRANS THEN
EXISTS_TAC `&2 pow n * x <= &2 pow n * y` THEN CONJ_TAC THENL
[SIMP_TAC[REAL_LE_LMUL_EQ; REAL_POW_LT; REAL_OF_NUM_LT; ARITH];
POP_ASSUM_LIST(MP_TAC o end_itlist CONJ) THEN REAL_ARITH_TAC]);;
let REALCALC_GT = prove
(`abs(a - &2 pow n * x) < &1 /\ abs(b - &2 pow n * y) < &1
==> &2 <= abs(a - b) ==> (x > y <=> a > b)`,
ONCE_REWRITE_TAC[CONJ_SYM; REAL_ABS_SUB] THEN
REWRITE_TAC[real_gt; REALCALC_LT]);;
let REALCALC_GE = prove
(`abs(a - &2 pow n * x) < &1 /\ abs(b - &2 pow n * y) < &1
==> &2 <= abs(a - b) ==> (x >= y <=> a >= b)`,
ONCE_REWRITE_TAC[CONJ_SYM; REAL_ABS_SUB] THEN
REWRITE_TAC[real_ge; REALCALC_LE]);;
let REALCALC_EQ = prove
(`abs(a - &2 pow n * x) < &1 /\ abs(b - &2 pow n * y) < &1
==> &2 <= abs(a - b) ==> ((x = y) <=> F)`,
ASM_CASES_TAC `x:real = y` THEN ASM_REWRITE_TAC[] THEN REAL_ARITH_TAC);;
let realcalc_rel_conv =
let pops =
[`(<)`,(</); `(<=)`,(<=/);
`(>)`,(>/); `(>=)`,(>=/);
`(=):real->real->bool`,(=/)] in
let rec find_n rfn1 rfn2 n =
if n >/ Int 1000 then
failwith "realcalc_rel_conv: too close to discriminate" else
if abs_num(raw_eval rfn1 n -/ raw_eval rfn2 n) >=/ Int 4 then n
else find_n rfn1 rfn2 (n +/ Int 1) in
fun tm ->
let lop,r = dest_comb tm in
let op,l = dest_comb lop in
let pop =
try assoc op pops
with Failure _ -> failwith "realcalc_rel_conv: unknown operator" in
let rfn1,tfn1 = REALCALC_CONV l
and rfn2,tfn2 = REALCALC_CONV r in
let n = find_n rfn1 rfn2 (Int 1) in
pop (raw_eval rfn1 n) (raw_eval rfn2 n);;
let REALCALC_REL_CONV =
let pths =
[`(<)`,REALCALC_LT; `(<=)`,REALCALC_LE;
`(>)`,REALCALC_GT; `(>=)`,REALCALC_GE;
`(=):real->real->bool`,REALCALC_EQ] in
let rec find_n rfn1 rfn2 n =
if n >/ Int 1000 then
failwith "realcalc_rel_conv: too close to discriminate" else
if abs_num(raw_eval rfn1 n -/ raw_eval rfn2 n) >=/ Int 4 then n
else find_n rfn1 rfn2 (n +/ Int 1) in
fun tm ->
let lop,r = dest_comb tm in
let op,l = dest_comb lop in
let pth = try assoc op pths
with Failure _ -> failwith "realcalc_rel_conv: unknown operator" in
let rfn1,tfn1 = REALCALC_CONV l
and rfn2,tfn2 = REALCALC_CONV r in
let n = find_n rfn1 rfn2 (Int 1) in
let th1 = thm_eval tfn1 n
and th2 = thm_eval tfn2 n in
let th3 = MATCH_MP pth (CONJ th1 th2) in
let th4 = MP th3 (EQT_ELIM(REAL_INT_REDUCE_CONV(lhand(concl th3)))) in
CONV_RULE(RAND_CONV REAL_RAT_REDUCE_CONV) th4;;
|