context: It is impossible that Gertrude is a sheep. It is almost certain that Antoine is hungry. It is almost certain that Julius is a frog. It is unlikely that if 'Gertrude is a sheep' or 'Julius is a frog' or both then Greg is white. It is probable that if either 'Gertrude is a sheep' or 'Julius is a frog' but not both then John discarded the apple. It is highly likely that if either 'Gertrude is a sheep' or 'Antoine is hungry' but not both then Brian is yellow.
hypothesis: We believe that either 'Greg is white' or 'Julius is a frog' but not both.
valid_hypothesis: We believe that either 'Greg is white' or 'Julius is a frog' but not both.
invalid_hypothesis: It is improbable that either 'Greg is white' or 'Julius is a frog' 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
    0.0::factA.
    0.95::factB.
    0.95::factC.
    %hop1
    0.2::factX:-or(factA,factC).
    0.7::factY:-xor(factA,factC).
    0.9::factZ:-xor(factA,factB).
  
    %hop2
    conclusion:-xor(factX,factC).
  
    query(conclusion).
    
hypothesis_assertion: Either 'Greg is white' or 'Julius is a frog' but not both.