There is a very good chance that Lily is a swan. There is little chance that Julius is a rhino. It is certain that Winona is a sheep. It is improbable that if 'Julius is a rhino' or 'Lily is a swan' or both then Emily is a sheep. It is impossible that if 'Julius is a rhino' or 'Winona is a sheep' or both then Bernhard is white. It is improbable that if either 'Lily is a swan' or 'Julius is a rhino' but not both then John dropped the milk.
It is impossible that either 'Lily is a swan' or 'Julius is a rhino' but not both.
We believe that either 'Lily is a swan' or 'Julius is a rhino' but not both.
It is impossible that either 'Lily is a swan' or 'Julius is a rhino' 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.
  0.1::factB.
  1.0::factC.
  %hop1
  0.1::factX:-or(factB,factA).
  0.0::factY:-or(factB,factC).
  0.1::factZ:-xor(factA,factB).

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

  query(conclusion).
  
Either 'Lily is a swan' or 'Julius is a rhino' but not both.