It is unlikely that Greg is white. It is likely that Winona is a cat. We believe that Bernhard is a swan. It is almost certain that if 'Winona is a cat and Bernhard is a swan' then Emily is a sheep. It is highly likely that if 'Winona is a cat' or 'Bernhard is a swan' or both then Julius is a frog. It is probably the case that if 'Bernhard is a swan and Winona is a cat' then Mary went to the office.
Chances are about even that either 'Bernhard is a swan' or 'Winona is a cat' but not both.
Chances are about even that either 'Bernhard is a swan' or 'Winona is a cat' but not both.
There is almost no chance that either 'Bernhard is a swan' or 'Winona is a cat' 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.
  0.7::factB.
  0.75::factC.
  %hop1
  0.95::factX:-and(factB,factC).
  0.9::factY:-or(factB,factC).
  0.7::factZ:-and(factC,factB).

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

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