context: It is almost certain that Sandra dropped the milk. There is little chance that Greg is a frog. It is likely that Lily is yellow. We believe that if 'Greg is a frog' or 'Sandra dropped the milk' or both then Brian is a lion. It is highly unlikely that if 'Sandra dropped the milk' or 'Greg is a frog' or both then Bernhard is a frog. It is almost certain that if 'Lily is yellow' or 'Sandra dropped the milk' or both then Mary discarded the milk.
hypothesis: It is certain that either 'Brian is a lion' or 'Sandra dropped the milk' but not both.
valid_hypothesis: It is probably not the case that either 'Brian is a lion' or 'Sandra dropped the milk' but not both.
invalid_hypothesis: It is certain that either 'Brian is a lion' or 'Sandra dropped the milk' 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.
    0.1::factB.
    0.7::factC.
    %hop1
    0.75::factX:-or(factB,factA).
    0.05::factY:-or(factA,factB).
    0.95::factZ:-or(factC,factA).
  
    %hop2
    conclusion:-xor(factX,factA).
  
    query(conclusion).
    
hypothesis_assertion: Either 'Brian is a lion' or 'Sandra dropped the milk' but not both.