context: It is unlikely that Fred left the football. It is certain that Bernhard is gray. It is almost certain that John discarded the apple.
hypothesis: We believe that either 'John discarded the apple' or 'Fred left the football' but not both.
valid_hypothesis: We believe that either 'John discarded the apple' or 'Fred left the football' but not both.
invalid_hypothesis: There is little chance that either 'John discarded the apple' or 'Fred left the football' 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
    0.2::factA.
    1.0::factB.
    0.95::factC.
    
  
    %hop2
    conclusion:-xor(factC,factA).
  
    query(conclusion).
    
hypothesis_assertion: Either 'John discarded the apple' or 'Fred left the football' but not both.