context: It is highly unlikely that John dropped the apple. There is almost no chance that Brian is a swan. It is likely that Greg is green.
hypothesis: It is impossible that either 'John dropped the apple' or 'Greg is green' but not both.
valid_hypothesis: It is probably the case that either 'John dropped the apple' or 'Greg is green' but not both.
invalid_hypothesis: It is impossible that either 'John dropped the apple' or 'Greg is green' 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
    0.05::factA.
    0.02::factB.
    0.7::factC.
    
  
    %hop2
    conclusion:-xor(factA,factC).
  
    query(conclusion).
    
hypothesis_assertion: Either 'John dropped the apple' or 'Greg is green' but not both.