context: Chances are slight that Julius is yellow. It is probably not the case that John dropped the apple. Chances are about even that Lily is a rhino. There is almost no chance that if either 'John dropped the apple' or 'Lily is a rhino' but not both then Bernhard is a swan. It is likely that if either 'Julius is yellow' or 'John dropped the apple' but not both then Winona is a sheep. It is probably the case that if 'Lily is a rhino' or 'Julius is yellow' or both then Greg is gray.
hypothesis: It is probable that 'Greg is gray and Winona is a sheep'.
valid_hypothesis: There is little chance that 'Greg is gray and Winona is a sheep'.
invalid_hypothesis: It is probable that 'Greg is gray and Winona is a sheep'.
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.
    0.25::factB.
    0.5::factC.
    %hop1
    0.02::factX:-xor(factB,factC).
    0.7::factY:-xor(factA,factB).
    0.7::factZ:-or(factC,factA).
  
    %hop2
    conclusion:-and(factZ,factY).
  
    query(conclusion).
    
hypothesis_assertion: 'Greg is gray and Winona is a sheep'.