It is probably not the case that Brian is yellow. There is little chance that John dropped the milk. There is a better than even chance that Julius is a swan. It is impossible that if 'Julius is a swan' or 'John dropped the milk' or both then Mary went to the kitchen. It is impossible that if 'Julius is a swan' or 'John dropped the milk' or both then Bernhard is a frog. It is probable that if either 'Julius is a swan' or 'Brian is yellow' but not both then Greg is a frog.
It is improbable that 'John dropped the milk' or 'Julius is a swan' or both.
There is a better than even chance that 'John dropped the milk' or 'Julius is a swan' or both.
It is improbable that 'John dropped the milk' or 'Julius 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
  0.25::factA.
  0.1::factB.
  0.6::factC.
  %hop1
  0.0::factX:-or(factC,factB).
  0.0::factY:-or(factC,factB).
  0.7::factZ:-xor(factC,factA).

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

  query(conclusion).
  
'John dropped the milk' or 'Julius is a swan' or both.