context: There is little chance that Brian is white. It is impossible that Jessica is a cat. It is certain that Greg is a swan. It is highly likely that if 'Greg is a swan' or 'Brian is white' or both then Bill got the milk there. We doubt that if 'Jessica is a cat' or 'Greg is a swan' or both then Bernhard is a rhino. It is improbable that if 'Brian is white' or 'Jessica is a cat' or both then Mary took the football.
hypothesis: It is probably the case that either 'Greg is a swan' or 'Bill got the milk there' but not both.
valid_hypothesis: It is improbable that either 'Greg is a swan' or 'Bill got the milk there' but not both.
invalid_hypothesis: It is probably the case that either 'Greg is a swan' or 'Bill got the milk there' 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
    0.1::factA.
    0.0::factB.
    1.0::factC.
    %hop1
    0.9::factX:-or(factC,factA).
    0.2::factY:-or(factB,factC).
    0.1::factZ:-or(factA,factB).
  
    %hop2
    conclusion:-xor(factC,factX).
  
    query(conclusion).
    
hypothesis_assertion: Either 'Greg is a swan' or 'Bill got the milk there' but not both.