It is probably the case that Julius is yellow. It is likely that John grabbed the apple. It is certain that Emily is a wolf. There is a better than even chance that if 'Emily is a wolf' or 'John grabbed the apple' or both then Gertrude is a sheep. Chances are slight that if either 'John grabbed the apple' or 'Julius is yellow' but not both then Lily is a frog. Chances are about even that if 'John grabbed the apple and Emily is a wolf' then Bernhard is a swan.
Chances are about even that either 'Emily is a wolf' or 'Gertrude is a sheep' but not both.
Chances are about even that either 'Emily is a wolf' or 'Gertrude is a sheep' but not both.
It is certain that either 'Emily is a wolf' or 'Gertrude is a sheep' 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
  0.7::factA.
  0.7::factB.
  1.0::factC.
  %hop1
  0.6::factX:-or(factC,factB).
  0.1::factY:-xor(factB,factA).
  0.5::factZ:-and(factB,factC).

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

  query(conclusion).
  
Either 'Emily is a wolf' or 'Gertrude is a sheep' but not both.