context: It is likely that John got the milk. It is probable that Brian is a swan. Chances are about even that Greg is yellow. There is little chance that if either 'Brian is a swan' or 'John got the milk' but not both then Jessica is a cat. It is unlikely that if 'Greg is yellow and Brian is a swan' then Bill went to the garden. It is impossible that if 'John got the milk and Brian is a swan' then Bernhard is a rhino.
hypothesis: It is probable that either 'Bernhard is a rhino' or 'John got the milk' but not both.
valid_hypothesis: It is probable that either 'Bernhard is a rhino' or 'John got the milk' but not both.
invalid_hypothesis: It is improbable that either 'Bernhard is a rhino' or 'John got 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
    0.7::factA.
    0.7::factB.
    0.5::factC.
    %hop1
    0.1::factX:-xor(factB,factA).
    0.2::factY:-and(factC,factB).
    0.0::factZ:-and(factA,factB).
  
    %hop2
    conclusion:-xor(factZ,factA).
  
    query(conclusion).
    
hypothesis_assertion: Either 'Bernhard is a rhino' or 'John got the milk' but not both.