It is probable that Bernhard is gray. It is certain that Lily is a rhino. It is probable that Mary took the milk. It is probably not the case that if 'Bernhard is gray and Lily is a rhino' then John went to the hallway. It is improbable that if 'Mary took the milk and Bernhard is gray' then Gertrude is a cat. We doubt that if either 'Bernhard is gray' or 'Lily is a rhino' but not both then Winona is a sheep.
There is almost no chance that 'John went to the hallway and Gertrude is a cat'.
There is almost no chance that 'John went to the hallway and Gertrude is a cat'.
There is a very good chance that 'John went to the hallway and Gertrude is a cat'.

  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
  0.7::factA.
  1.0::factB.
  0.7::factC.
  %hop1
  0.25::factX:-and(factA,factB).
  0.1::factY:-and(factC,factA).
  0.2::factZ:-xor(factA,factB).

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

  query(conclusion).
  
'John went to the hallway and Gertrude is a cat'.