context: Chances are about even that Bernhard is a frog. We doubt that John went to the hallway. It is probable that Gertrude is a sheep.
hypothesis: It is impossible that either 'John went to the hallway' or 'Bernhard is a frog' but not both.
valid_hypothesis: Chances are about even that either 'John went to the hallway' or 'Bernhard is a frog' but not both.
invalid_hypothesis: It is impossible that either 'John went to the hallway' or 'Bernhard 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
    0.5::factA.
    0.2::factB.
    0.7::factC.
    
  
    %hop2
    conclusion:-xor(factB,factA).
  
    query(conclusion).
    
hypothesis_assertion: Either 'John went to the hallway' or 'Bernhard is a frog' but not both.