We believe that Greg is white. It is almost certain that Bernhard is a swan. There is a better than even chance that Mary went to the hallway. It is probably not the case that if 'Mary went to the hallway' or 'Bernhard is a swan' or both then Lily is a lion. Chances are slight that if either 'Bernhard is a swan' or 'Greg is white' but not both then Winona is a cat. It is impossible that if 'Greg is white and Bernhard is a swan' then Brian is gray.
Chances are about even that either 'Bernhard is a swan' or 'Mary went to the hallway' but not both.
Chances are about even that either 'Bernhard is a swan' or 'Mary went to the hallway' but not both.
It is impossible that either 'Bernhard is a swan' or 'Mary went to the hallway' 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.
  0.95::factB.
  0.6::factC.
  %hop1
  0.25::factX:-or(factC,factB).
  0.1::factY:-xor(factB,factA).
  0.0::factZ:-and(factA,factB).

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

  query(conclusion).
  
Either 'Bernhard is a swan' or 'Mary went to the hallway' but not both.