context: We doubt that Bernhard is white. It is certain that Brian is a frog. We doubt that Jeff discarded the milk.
hypothesis: There is a very good chance that either 'Bernhard is white' or 'Brian is a frog' but not both.
valid_hypothesis: There is a very good chance that either 'Bernhard is white' or 'Brian is a frog' but not both.
invalid_hypothesis: We doubt that either 'Bernhard is white' or 'Brian 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
    0.2::factA.
    1.0::factB.
    0.2::factC.
    
  
    %hop2
    conclusion:-xor(factA,factB).
  
    query(conclusion).
    
hypothesis_assertion: Either 'Bernhard is white' or 'Brian is a frog' but not both.