context: It is highly unlikely that Brian is white. There is little chance that Lily is a swan. It is probably the case that Greg is a rhino. We doubt that if either 'Greg is a rhino' or 'Brian is white' but not both then Gertrude is a cat. We doubt that if 'Brian is white' or 'Lily is a swan' or both then Mary dropped the apple. It is highly unlikely that if 'Lily is a swan and Brian is white' then John took the football.
hypothesis: There is a very good chance that either 'Brian is white' or 'Mary dropped the apple' but not both.
valid_hypothesis: It is highly unlikely that either 'Brian is white' or 'Mary dropped the apple' but not both.
invalid_hypothesis: There is a very good chance that either 'Brian is white' or 'Mary dropped the apple' 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
    0.05::factA.
    0.1::factB.
    0.7::factC.
    %hop1
    0.2::factX:-xor(factC,factA).
    0.2::factY:-or(factA,factB).
    0.05::factZ:-and(factB,factA).
  
    %hop2
    conclusion:-xor(factA,factY).
  
    query(conclusion).
    
hypothesis_assertion: Either 'Brian is white' or 'Mary dropped the apple' but not both.