context: It is highly likely that John took the apple. It is unlikely that Mary went to the office. It is probably the case that Bernhard is yellow.
hypothesis: We believe that either 'Mary went to the office' or 'John took the apple' but not both.
valid_hypothesis: We believe that either 'Mary went to the office' or 'John took the apple' but not both.
invalid_hypothesis: We doubt that either 'Mary went to the office' or 'John took the apple' 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
    0.9::factA.
    0.2::factB.
    0.7::factC.
    
  
    %hop2
    conclusion:-xor(factB,factA).
  
    query(conclusion).
    
hypothesis_assertion: Either 'Mary went to the office' or 'John took the apple' but not both.