It is unlikely that Gertrude is a sheep. There is almost no chance that Julius is a lion. It is almost certain that Bernhard is a frog. Chances are slight that if 'Julius is a lion' or 'Gertrude is a sheep' or both then Greg is a rhino. It is highly likely that if 'Julius is a lion and Gertrude is a sheep' then Brian is white. We believe that if 'Julius is a lion' or 'Bernhard is a frog' or both then John went to the garden.
There is a very good chance that either 'Gertrude is a sheep' or 'Julius is a lion' but not both.
It is unlikely that either 'Gertrude is a sheep' or 'Julius is a lion' but not both.
There is a very good chance that either 'Gertrude is a sheep' or 'Julius is a lion' 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.
  0.02::factB.
  0.95::factC.
  %hop1
  0.1::factX:-or(factB,factA).
  0.9::factY:-and(factB,factA).
  0.75::factZ:-or(factB,factC).

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

  query(conclusion).
  
Either 'Gertrude is a sheep' or 'Julius is a lion' but not both.