context: We doubt that Julius is a swan. It is highly likely that Gertrude is a sheep. It is certain that Bernhard is white. We believe that if either 'Bernhard is white' or 'Julius is a swan' but not both then Greg is white. We doubt that if 'Gertrude is a sheep' or 'Bernhard is white' or both then Sandra dropped the milk. It is likely that if 'Bernhard is white and Julius is a swan' then John got the apple.
hypothesis: It is impossible that 'Greg is white and Bernhard is white'.
valid_hypothesis: There is a better than even chance that 'Greg is white and Bernhard is white'.
invalid_hypothesis: It is impossible that 'Greg is white and Bernhard is white'.
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
    0.2::factA.
    0.9::factB.
    1.0::factC.
    %hop1
    0.75::factX:-xor(factC,factA).
    0.2::factY:-or(factB,factC).
    0.7::factZ:-and(factC,factA).
  
    %hop2
    conclusion:-and(factX,factC).
  
    query(conclusion).
    
hypothesis_assertion: 'Greg is white and Bernhard is white'.