It is improbable that Mary grabbed the milk. It is highly unlikely that Brian is a swan. It is probably not the case that Bernhard is green. We doubt that if 'Mary grabbed the milk and Brian is a swan' then Daniel got the football. There is almost no chance that if either 'Mary grabbed the milk' or 'Brian is a swan' but not both then Gertrude is a wolf. It is improbable that if 'Brian is a swan' or 'Mary grabbed the milk' or both then John is in the garden.
It is certain that 'Brian is a swan' or 'Mary grabbed the milk' or both.
There is little chance that 'Brian is a swan' or 'Mary grabbed the milk' or both.
It is certain that 'Brian is a swan' or 'Mary grabbed the milk' 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
  0.1::factA.
  0.05::factB.
  0.25::factC.
  %hop1
  0.2::factX:-and(factA,factB).
  0.02::factY:-xor(factA,factB).
  0.1::factZ:-or(factB,factA).

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

  query(conclusion).
  
'Brian is a swan' or 'Mary grabbed the milk' or both.