It is almost certain that Brian is a lion. Chances are about even that Emily is a cat. It is probably the case that Mary went to the garden. There is little chance that if 'Brian is a lion and Mary went to the garden' then Lily is green. Chances are slight that if 'Brian is a lion' or 'Mary went to the garden' or both then John dropped the milk. It is improbable that if 'Mary went to the garden' or 'Emily is a cat' or both then Bernhard is a frog.
We believe that either 'Mary went to the garden' or 'Brian is a lion' but not both.
It is probably not the case that either 'Mary went to the garden' or 'Brian is a lion' but not both.
We believe that either 'Mary went to the garden' or 'Brian is a lion' but not 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
  0.95::factA.
  0.5::factB.
  0.7::factC.
  %hop1
  0.1::factX:-and(factA,factC).
  0.1::factY:-or(factA,factC).
  0.1::factZ:-or(factC,factB).

  %hop2
  conclusion:-xor(factC,factA).

  query(conclusion).
  
Either 'Mary went to the garden' or 'Brian is a lion' but not both.