There is a better than even chance that Gertrude is a cat. It is certain that Brian is a rhino. It is highly likely that Lily is a swan. Chances are about even that if 'Gertrude is a cat' or 'Lily is a swan' or both then Winona is a sheep. There is little chance that if either 'Lily is a swan' or 'Gertrude is a cat' but not both then John dropped the milk. It is highly likely that if either 'Gertrude is a cat' or 'Lily is a swan' but not both then Greg is yellow.
There is a very good chance that 'Winona is a sheep' or 'Gertrude is a cat' or both.
There is a very good chance that 'Winona is a sheep' or 'Gertrude is a cat' or both.
We doubt that 'Winona is a sheep' or 'Gertrude is a cat' 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
  0.6::factA.
  1.0::factB.
  0.9::factC.
  %hop1
  0.5::factX:-or(factA,factC).
  0.1::factY:-xor(factC,factA).
  0.9::factZ:-xor(factA,factC).

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

  query(conclusion).
  
'Winona is a sheep' or 'Gertrude is a cat' or both.