Chances are about even that Brian is white. It is unlikely that Winona is a cat. We believe that Bernhard is a rhino. There is almost no chance that if 'Winona is a cat' or 'Bernhard is a rhino' or both then Emily is a mouse. It is probably not the case that if 'Bernhard is a rhino and Winona is a cat' then Lily is a swan. Chances are slight that if either 'Brian is white' or 'Bernhard is a rhino' but not both then Mary dropped the milk.
It is probably not the case that either 'Winona is a cat' or 'Mary dropped the milk' but not both.
It is probably not the case that either 'Winona is a cat' or 'Mary dropped the milk' but not both.
There is a very good chance that either 'Winona is a cat' or 'Mary dropped the milk' 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
  0.5::factA.
  0.2::factB.
  0.75::factC.
  %hop1
  0.02::factX:-or(factB,factC).
  0.25::factY:-and(factC,factB).
  0.1::factZ:-xor(factA,factC).

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

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