We believe that John discarded the milk. It is highly likely that Julius is white. It is improbable that Bernhard is a swan. It is impossible that if 'Bernhard is a swan and John discarded the milk' then Winona is a wolf. We doubt that if either 'John discarded the milk' or 'Bernhard is a swan' but not both then Mary left the football. We believe that if 'Bernhard is a swan and Julius is white' then Lily is a frog.
It is improbable that either 'Winona is a wolf' or 'Bernhard is a swan' but not both.
It is improbable that either 'Winona is a wolf' or 'Bernhard is a swan' but not both.
There is a better than even chance that either 'Winona is a wolf' 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
  0.75::factA.
  0.9::factB.
  0.1::factC.
  %hop1
  0.0::factX:-and(factC,factA).
  0.2::factY:-xor(factA,factC).
  0.75::factZ:-and(factC,factB).

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

  query(conclusion).
  
Either 'Winona is a wolf' or 'Bernhard is a swan' but not both.