context: Chances are about even that John took the apple. It is likely that Greg is a swan. It is highly unlikely that Julius is yellow.
hypothesis: It is probable that either 'Julius is yellow' or 'Greg is a swan' but not both.
valid_hypothesis: It is probable that either 'Julius is yellow' or 'Greg is a swan' but not both.
invalid_hypothesis: It is highly unlikely that either 'Julius is yellow' or 'Greg 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
    0.5::factA.
    0.7::factB.
    0.05::factC.
    
  
    %hop2
    conclusion:-xor(factC,factB).
  
    query(conclusion).
    
hypothesis_assertion: Either 'Julius is yellow' or 'Greg is a swan' but not both.