Chances are about even that Lily is a swan. It is highly likely that Sandra left the milk. It is probable that Bernhard is gray. There is little chance that if 'Lily is a swan' or 'Sandra left the milk' or both then Winona is a sheep. There is a better than even chance that if 'Lily is a swan and Bernhard is gray' then Gertrude is a wolf. It is certain that if either 'Lily is a swan' or 'Bernhard is gray' but not both then John moved to the office.
It is impossible that 'John moved to the office and Gertrude is a wolf'.
It is impossible that 'John moved to the office and Gertrude is a wolf'.
There is a very good chance that 'John moved to the office and Gertrude is a wolf'.

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

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

  query(conclusion).
  
'John moved to the office and Gertrude is a wolf'.