Chances are slight that John picked up the milk. There is a very good chance that Gertrude is a cat. There is a very good chance that Brian is white. It is highly unlikely that if either 'Brian is white' or 'John picked up the milk' but not both then Mary moved to the garden. It is probably the case that if 'Gertrude is a cat' or 'Brian is white' or both then Daniel dropped the apple. It is unlikely that if 'John picked up the milk' or 'Gertrude is a cat' or both then Lily is green.
There is a very good chance that 'Brian is white' or 'John picked up the milk' or both.
There is a very good chance that 'Brian is white' or 'John picked up the milk' or both.
We doubt that 'Brian is white' or 'John picked up 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.
  0.8::factB.
  0.8::factC.
  %hop1
  0.05::factX:-xor(factC,factA).
  0.7::factY:-or(factB,factC).
  0.2::factZ:-or(factA,factB).

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

  query(conclusion).
  
'Brian is white' or 'John picked up the milk' or both.