context: Chances are about even that Brian is a frog. It is certain that Lily is gray. It is impossible that Greg is white. It is improbable that if 'Brian is a frog' or 'Greg is white' or both then Gertrude is a sheep. It is improbable that if 'Brian is a frog and Greg is white' then Julius is yellow. Chances are slight that if 'Greg is white' or 'Lily is gray' or both then John moved to the office.
hypothesis: There is a very good chance that 'Greg is white and Lily is gray'.
valid_hypothesis: It is impossible that 'Greg is white and Lily is gray'.
invalid_hypothesis: There is a very good chance that 'Greg is white and Lily is gray'.
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
    0.5::factA.
    1.0::factB.
    0.0::factC.
    %hop1
    0.1::factX:-or(factA,factC).
    0.1::factY:-and(factA,factC).
    0.1::factZ:-or(factC,factB).
  
    %hop2
    conclusion:-and(factC,factB).
  
    query(conclusion).
    
hypothesis_assertion: 'Greg is white and Lily is gray'.