context: It is certain that Julius is gray. It is impossible that Lily is a swan. It is impossible that Mary dropped the milk.
hypothesis: It is impossible that either 'Mary dropped the milk' or 'Lily is a swan' but not both.
valid_hypothesis: It is impossible that either 'Mary dropped the milk' or 'Lily is a swan' but not both.
invalid_hypothesis: It is highly likely that either 'Mary dropped the milk' or 'Lily 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
    1.0::factA.
    0.0::factB.
    0.0::factC.
    
  
    %hop2
    conclusion:-xor(factC,factB).
  
    query(conclusion).
    
hypothesis_assertion: Either 'Mary dropped the milk' or 'Lily is a swan' but not both.