We doubt that Winona is a cat. It is probably the case that John got the apple. There is little chance that Mary grabbed the milk. There is a very good chance that if 'Mary grabbed the milk' or 'Winona is a cat' or both then Gertrude is a sheep. We believe that if either 'Mary grabbed the milk' or 'Winona is a cat' but not both then Lily is a rhino. There is little chance that if 'Mary grabbed the milk and Winona is a cat' then Brian is a swan.
There is a very good chance that 'Gertrude is a sheep' or 'Brian is a swan' or both.
We doubt that 'Gertrude is a sheep' or 'Brian is a swan' or both.
There is a very good chance that 'Gertrude is a sheep' or 'Brian is a swan' or both.

  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
  0.2::factA.
  0.7::factB.
  0.1::factC.
  %hop1
  0.8::factX:-or(factC,factA).
  0.75::factY:-xor(factC,factA).
  0.1::factZ:-and(factC,factA).

  %hop2
  conclusion:-or(factX,factZ).

  query(conclusion).
  
'Gertrude is a sheep' or 'Brian is a swan' or both.