We doubt that Emily is a wolf. It is probably not the case that Daniel got the milk. It is highly likely that John left the apple. It is probably not the case that if 'Emily is a wolf and Daniel got the milk' then Greg is yellow. It is certain that if 'Emily is a wolf' or 'Daniel got the milk' or both then Bernhard is a swan. Chances are about even that if 'Daniel got the milk' or 'Emily is a wolf' or both then Mary dropped the milk.
It is probably the case that either 'Mary dropped the milk' or 'Bernhard is a swan' but not both.
We doubt that either 'Mary dropped the milk' or 'Bernhard is a swan' but not both.
It is probably the case that either 'Mary dropped the milk' or 'Bernhard is a swan' 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
  0.2::factA.
  0.25::factB.
  0.9::factC.
  %hop1
  0.25::factX:-and(factA,factB).
  1.0::factY:-or(factA,factB).
  0.5::factZ:-or(factB,factA).

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

  query(conclusion).
  
Either 'Mary dropped the milk' or 'Bernhard is a swan' but not both.