context: There is little chance that Greg is white. It is certain that Sandra dropped the milk. We believe that Brian is a swan. There is little chance that if 'Brian is a swan' or 'Greg is white' or both then Mary went to the office. It is improbable that if either 'Greg is white' or 'Sandra dropped the milk' but not both then Gertrude is a sheep. It is impossible that if 'Brian is a swan' or 'Greg is white' or both then Bernhard is a frog.
hypothesis: It is highly likely that either 'Sandra dropped the milk' or 'Gertrude is a sheep' but not both.
valid_hypothesis: It is highly likely that either 'Sandra dropped the milk' or 'Gertrude is a sheep' but not both.
invalid_hypothesis: It is unlikely that either 'Sandra dropped the milk' or 'Gertrude is a sheep' 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
    0.1::factA.
    1.0::factB.
    0.75::factC.
    %hop1
    0.1::factX:-or(factC,factA).
    0.1::factY:-xor(factA,factB).
    0.0::factZ:-or(factC,factA).
  
    %hop2
    conclusion:-xor(factB,factY).
  
    query(conclusion).
    
hypothesis_assertion: Either 'Sandra dropped the milk' or 'Gertrude is a sheep' but not both.