It is certain that Brian is yellow. It is certain that Mary grabbed the milk. It is improbable that Lily is a rhino. Chances are slight that if 'Brian is yellow' or 'Mary grabbed the milk' or both then Emily is a wolf. It is likely that if either 'Mary grabbed the milk' or 'Lily is a rhino' but not both then Julius is a swan. It is improbable that if either 'Lily is a rhino' or 'Brian is yellow' but not both then John dropped the milk.
There is a better than even chance that either 'Julius is a swan' or 'Emily is a wolf' but not both.
There is a better than even chance that either 'Julius is a swan' or 'Emily is a wolf' but not both.
There is almost no chance that either 'Julius is a swan' or 'Emily is a wolf' 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
  1.0::factA.
  1.0::factB.
  0.1::factC.
  %hop1
  0.1::factX:-or(factA,factB).
  0.7::factY:-xor(factB,factC).
  0.1::factZ:-xor(factC,factA).

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

  query(conclusion).
  
Either 'Julius is a swan' or 'Emily is a wolf' but not both.