context: It is improbable that Winona is a sheep. Chances are about even that Julius is green. There is little chance that Bernhard is a swan. It is likely that if 'Bernhard is a swan' or 'Winona is a sheep' or both then Brian is a rhino. It is impossible that if either 'Bernhard is a swan' or 'Julius is green' but not both then Mary grabbed the milk. It is almost certain that if 'Bernhard is a swan and Julius is green' then Greg is a frog.
hypothesis: It is probably the case that either 'Mary grabbed the milk' or 'Brian is a rhino' but not both.
valid_hypothesis: It is improbable that either 'Mary grabbed the milk' or 'Brian is a rhino' but not both.
invalid_hypothesis: It is probably the case that either 'Mary grabbed the milk' or 'Brian is a rhino' 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.
    0.5::factB.
    0.1::factC.
    %hop1
    0.7::factX:-or(factC,factA).
    0.0::factY:-xor(factC,factB).
    0.95::factZ:-and(factC,factB).
  
    %hop2
    conclusion:-xor(factY,factX).
  
    query(conclusion).
    
hypothesis_assertion: Either 'Mary grabbed the milk' or 'Brian is a rhino' but not both.