context: It is almost certain that Julius is green. Chances are about even that Bernhard is a lion. It is certain that Mary discarded the milk. It is almost certain that if 'Bernhard is a lion' or 'Mary discarded the milk' or both then Greg is a swan. There is almost no chance that if 'Bernhard is a lion and Mary discarded the milk' then Jessica is a cat. It is unlikely that if 'Julius is green and Bernhard is a lion' then John left the football.
hypothesis: It is probably the case that either 'Mary discarded the milk' or 'Greg is a swan' but not both.
valid_hypothesis: It is highly unlikely that either 'Mary discarded the milk' or 'Greg is a swan' but not both.
invalid_hypothesis: It is probably the case that either 'Mary discarded the milk' or 'Greg is a swan' 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.
    0.5::factB.
    1.0::factC.
    %hop1
    0.95::factX:-or(factB,factC).
    0.02::factY:-and(factB,factC).
    0.2::factZ:-and(factA,factB).
  
    %hop2
    conclusion:-xor(factC,factX).
  
    query(conclusion).
    
hypothesis_assertion: Either 'Mary discarded the milk' or 'Greg is a swan' but not both.