It is highly unlikely that Bernhard is a frog. It is highly unlikely that Julius is gray. It is certain that Greg is a swan. It is highly likely that if either 'Greg is a swan' or 'Bernhard is a frog' but not both then Bill went to the kitchen. Chances are slight that if 'Greg is a swan' or 'Julius is gray' or both then Mary took the football. Chances are about even that if 'Greg is a swan' or 'Julius is gray' or both then Sandra left the milk.
It is improbable that 'Greg is a swan and Bill went to the kitchen'.
It is highly likely that 'Greg is a swan and Bill went to the kitchen'.
It is improbable that 'Greg is a swan and Bill went to the kitchen'.

  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
  0.05::factA.
  0.05::factB.
  1.0::factC.
  %hop1
  0.9::factX:-xor(factC,factA).
  0.1::factY:-or(factC,factB).
  0.5::factZ:-or(factC,factB).

  %hop2
  conclusion:-and(factC,factX).

  query(conclusion).
  
'Greg is a swan and Bill went to the kitchen'.