context: It is probably not the case that John got the milk. Chances are about even that Daniel dropped the apple. It is improbable that Fred is in the office.
hypothesis: It is probably the case that either 'John got the milk' or 'Fred is in the office' but not both.
valid_hypothesis: It is probably not the case that either 'John got the milk' or 'Fred is in the office' but not both.
invalid_hypothesis: It is probably the case that either 'John got the milk' or 'Fred is in 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
    0.25::factA.
    0.5::factB.
    0.1::factC.
    
  
    %hop2
    conclusion:-xor(factA,factC).
  
    query(conclusion).
    
hypothesis_assertion: Either 'John got the milk' or 'Fred is in the office' but not both.