context: It is almost certain that Mary dropped the milk. It is probable that Greg is a frog. It is certain that Gertrude is a sheep. We doubt that if either 'Mary dropped the milk' or 'Greg is a frog' but not both then John put down the apple. It is likely that if 'Mary dropped the milk' or 'Gertrude is a sheep' or both then Brian is a rhino. It is certain that if either 'Gertrude is a sheep' or 'Greg is a frog' but not both then Sandra took the milk.
hypothesis: Chances are about even that either 'Gertrude is a sheep' or 'John put down the apple' but not both.
valid_hypothesis: It is almost certain that either 'Gertrude is a sheep' or 'John put down the apple' but not both.
invalid_hypothesis: Chances are about even that either 'Gertrude is a sheep' or 'John put down the apple' but not both.
problog: 
    and(A,B) :- A,B.
    or(A,B) :- A;B.
    nand(A,B) :- not(and(A,B)).
    nor(A,B) :- not(or(A,B)).
    xor(A,B) :- or(A,B), nand(A,B).
  
    %hop0
    0.95::factA.
    0.7::factB.
    1.0::factC.
    %hop1
    0.2::factX:-xor(factA,factB).
    0.7::factY:-or(factA,factC).
    1.0::factZ:-xor(factC,factB).
  
    %hop2
    conclusion:-xor(factC,factX).
  
    query(conclusion).
    
hypothesis_assertion: Either 'Gertrude is a sheep' or 'John put down the apple' but not both.