It is highly likely that Brian is white. It is highly unlikely that Gertrude is a sheep. It is probably the case that Bernhard is a swan. We believe that if 'Gertrude is a sheep' or 'Brian is white' or both then Daniel took the milk. It is probable that if 'Brian is white and Bernhard is a swan' then Mary went to the garden. It is likely that if either 'Gertrude is a sheep' or 'Bernhard is a swan' but not both then John left the apple.
It is highly unlikely that either 'Bernhard is a swan' or 'Gertrude is a sheep' but not both.
It is probably the case that either 'Bernhard is a swan' or 'Gertrude is a sheep' but not both.
It is highly unlikely that either 'Bernhard is a swan' or 'Gertrude is a sheep' 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
  0.9::factA.
  0.05::factB.
  0.7::factC.
  %hop1
  0.75::factX:-or(factB,factA).
  0.7::factY:-and(factA,factC).
  0.7::factZ:-xor(factB,factC).

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

  query(conclusion).
  
Either 'Bernhard is a swan' or 'Gertrude is a sheep' but not both.