It is certain that Greg is a swan. It is probably not the case that Sandra left the football. It is probably the case that Brian is a lion. It is probable that if 'Greg is a swan' or 'Sandra left the football' or both then John moved to the garden. It is impossible that if either 'Greg is a swan' or 'Brian is a lion' but not both then Gertrude is a sheep. There is almost no chance that if either 'Sandra left the football' or 'Greg is a swan' but not both then Bernhard is a frog.
It is probably not the case that either 'Gertrude is a sheep' or 'Sandra left the football' but not both.
It is probably not the case that either 'Gertrude is a sheep' or 'Sandra left the football' but not both.
It is almost certain that either 'Gertrude is a sheep' or 'Sandra left the football' 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.
  0.25::factB.
  0.7::factC.
  %hop1
  0.7::factX:-or(factA,factB).
  0.0::factY:-xor(factA,factC).
  0.02::factZ:-xor(factB,factA).

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

  query(conclusion).
  
Either 'Gertrude is a sheep' or 'Sandra left the football' but not both.