It is unlikely that John went to the bedroom. Chances are about even that Mary left the milk. It is certain that Greg is yellow. It is probably not the case that if 'John went to the bedroom and Mary left the milk' then Julius is a swan. It is improbable that if either 'Greg is yellow' or 'John went to the bedroom' but not both then Sumit is tired. There is little chance that if either 'Greg is yellow' or 'Mary left the milk' but not both then Lily is a rhino.
There is almost no chance that 'Mary left the milk' or 'John went to the bedroom' or both.
There is a better than even chance that 'Mary left the milk' or 'John went to the bedroom' or both.
There is almost no chance that 'Mary left the milk' or 'John went to the bedroom' 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.
  1.0::factC.
  %hop1
  0.25::factX:-and(factA,factB).
  0.1::factY:-xor(factC,factA).
  0.1::factZ:-xor(factC,factB).

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

  query(conclusion).
  
'Mary left the milk' or 'John went to the bedroom' or both.