We doubt that Mary left the milk. Chances are about even that Bernhard is a swan. We doubt that Brian is a rhino. There is a very good chance that if 'Mary left the milk' or 'Bernhard is a swan' or both then Winona is a wolf. There is almost no chance that if either 'Mary left the milk' or 'Brian is a rhino' but not both then Julius is white. It is almost certain that if either 'Mary left the milk' or 'Bernhard is a swan' but not both then John went to the garden.
There is a better than even chance that 'John went to the garden' or 'Brian is a rhino' or both.
There is a better than even chance that 'John went to the garden' or 'Brian is a rhino' or both.
There is almost no chance that 'John went to the garden' or 'Brian is a rhino' 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.
  0.5::factB.
  0.2::factC.
  %hop1
  0.8::factX:-or(factA,factB).
  0.02::factY:-xor(factA,factC).
  0.95::factZ:-xor(factA,factB).

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

  query(conclusion).
  
'John went to the garden' or 'Brian is a rhino' or both.