It is certain that Winona is a mouse. It is highly unlikely that Gertrude is a mouse. There is a very good chance that Greg is a swan. It is unlikely that if 'Greg is a swan and Winona is a mouse' then Julius is gray. Chances are about even that if 'Winona is a mouse and Gertrude is a mouse' then Brian is white. We doubt that if 'Greg is a swan and Gertrude is a mouse' then Daniel got the milk.
We doubt that either 'Winona is a mouse' or 'Julius is gray' but not both.
There is a very good chance that either 'Winona is a mouse' or 'Julius is gray' but not both.
We doubt that either 'Winona is a mouse' or 'Julius is gray' 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.
  0.05::factB.
  0.8::factC.
  %hop1
  0.2::factX:-and(factC,factA).
  0.5::factY:-and(factA,factB).
  0.2::factZ:-and(factC,factB).

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

  query(conclusion).
  
Either 'Winona is a mouse' or 'Julius is gray' but not both.