context: There is little chance that Fred is in the school. We believe that Lily is a swan. There is a very good chance that John dropped the apple. We doubt that if either 'Lily is a swan' or 'John dropped the apple' but not both then Bernhard is green. There is little chance that if either 'John dropped the apple' or 'Lily is a swan' but not both then Greg is a lion. It is almost certain that if 'Lily is a swan' or 'Fred is in the school' or both then Brian is white.
hypothesis: It is highly unlikely that either 'Brian is white' or 'Lily is a swan' but not both.
valid_hypothesis: It is highly unlikely that either 'Brian is white' or 'Lily is a swan' but not both.
invalid_hypothesis: It is probable that either 'Brian is white' 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
    0.1::factA.
    0.75::factB.
    0.8::factC.
    %hop1
    0.2::factX:-xor(factB,factC).
    0.1::factY:-xor(factC,factB).
    0.95::factZ:-or(factB,factA).
  
    %hop2
    conclusion:-xor(factZ,factB).
  
    query(conclusion).
    
hypothesis_assertion: Either 'Brian is white' or 'Lily is a swan' but not both.