context: It is certain that John went to the office. It is impossible that Greg is a frog. Chances are about even that Brian is white.
hypothesis: It is highly unlikely that either 'Greg is a frog' or 'John went to the office' but not both.
valid_hypothesis: It is certain that either 'Greg is a frog' or 'John went to the office' but not both.
invalid_hypothesis: It is highly unlikely that either 'Greg is a frog' or 'John went to the office' 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
    1.0::factA.
    0.0::factB.
    0.5::factC.
    
  
    %hop2
    conclusion:-xor(factB,factA).
  
    query(conclusion).
    
hypothesis_assertion: Either 'Greg is a frog' or 'John went to the office' but not both.