context: It is improbable that John went to the garden. It is probably the case that Greg is a rhino. There is a very good chance that Brian is a lion. It is unlikely that if either 'John went to the garden' or 'Greg is a rhino' but not both then Bernhard is a swan. It is probably not the case that if either 'John went to the garden' or 'Brian is a lion' but not both then Lily is white. Chances are about even that if 'Brian is a lion and John went to the garden' then Gertrude is a cat.
hypothesis: It is improbable that either 'Brian is a lion' or 'Gertrude is a cat' but not both.
valid_hypothesis: We believe that either 'Brian is a lion' or 'Gertrude is a cat' but not both.
invalid_hypothesis: It is improbable that either 'Brian is a lion' or 'Gertrude is a cat' 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.
    0.7::factB.
    0.8::factC.
    %hop1
    0.2::factX:-xor(factA,factB).
    0.25::factY:-xor(factA,factC).
    0.5::factZ:-and(factC,factA).
  
    %hop2
    conclusion:-xor(factC,factZ).
  
    query(conclusion).
    
hypothesis_assertion: Either 'Brian is a lion' or 'Gertrude is a cat' but not both.