It is improbable that Brian is a lion. There is almost no chance that Gertrude is a sheep. It is unlikely that Greg is white. It is almost certain that if 'Brian is a lion' or 'Gertrude is a sheep' or both then Jeff went to the garden. It is impossible that if 'Brian is a lion' or 'Gertrude is a sheep' or both then John discarded the milk. We believe that if either 'Brian is a lion' or 'Greg is white' but not both then Lily is a swan.
It is impossible that 'John discarded the milk and Lily is a swan'.
It is impossible that 'John discarded the milk and Lily is a swan'.
There is a very good chance that 'John discarded the milk and Lily is a swan'.

  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
  0.1::factA.
  0.02::factB.
  0.2::factC.
  %hop1
  0.95::factX:-or(factA,factB).
  0.0::factY:-or(factA,factB).
  0.75::factZ:-xor(factA,factC).

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

  query(conclusion).
  
'John discarded the milk and Lily is a swan'.