There is a very good chance that Brian is a lion. It is probably the case that Lily is white. We doubt that Greg is a rhino. It is likely that if 'Greg is a rhino and Brian is a lion' then Winona is a wolf. Chances are slight that if 'Brian is a lion' or 'Lily is white' or both then Mary got the milk. It is certain that if 'Brian is a lion and Lily is white' then Julius is gray.
We believe that either 'Mary got the milk' or 'Brian is a lion' but not both.
We believe that either 'Mary got the milk' or 'Brian is a lion' but not both.
Chances are slight that either 'Mary got the milk' 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
  0.8::factA.
  0.7::factB.
  0.2::factC.
  %hop1
  0.7::factX:-and(factC,factA).
  0.1::factY:-or(factA,factB).
  1.0::factZ:-and(factA,factB).

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

  query(conclusion).
  
Either 'Mary got the milk' or 'Brian is a lion' but not both.