context: It is highly unlikely that John picked up the milk. It is probably the case that Greg is a swan. Chances are about even that Sandra dropped the milk.
hypothesis: Chances are about even that either 'Greg is a swan' or 'Sandra dropped the milk' but not both.
valid_hypothesis: Chances are about even that either 'Greg is a swan' or 'Sandra dropped the milk' but not both.
invalid_hypothesis: It is impossible that either 'Greg is a swan' or 'Sandra dropped the milk' 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
    0.05::factA.
    0.7::factB.
    0.5::factC.
    
  
    %hop2
    conclusion:-xor(factB,factC).
  
    query(conclusion).
    
hypothesis_assertion: Either 'Greg is a swan' or 'Sandra dropped the milk' but not both.