context: Chances are about even that Greg is white. It is probably the case that Bernhard is a swan. We doubt that Jeff went to the garden. It is probably the case that if 'Jeff went to the garden' or 'Bernhard is a swan' or both then Brian is yellow. It is improbable that if 'Jeff went to the garden and Bernhard is a swan' then John took the football. There is almost no chance that if 'Greg is white' or 'Bernhard is a swan' or both then Bill moved to the office.
hypothesis: It is impossible that either 'Bernhard is a swan' or 'Jeff went to the garden' but not both.
valid_hypothesis: There is a better than even chance that either 'Bernhard is a swan' or 'Jeff went to the garden' but not both.
invalid_hypothesis: It is impossible that either 'Bernhard is a swan' or 'Jeff went to the garden' 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
    0.5::factA.
    0.7::factB.
    0.2::factC.
    %hop1
    0.7::factX:-or(factC,factB).
    0.1::factY:-and(factC,factB).
    0.02::factZ:-or(factA,factB).
  
    %hop2
    conclusion:-xor(factB,factC).
  
    query(conclusion).
    
hypothesis_assertion: Either 'Bernhard is a swan' or 'Jeff went to the garden' but not both.