We doubt that Mary went to the garden. There is little chance that Greg is yellow. It is improbable that Bernhard is a rhino. There is almost no chance that if 'Greg is yellow and Bernhard is a rhino' then Emily is a cat. It is certain that if 'Mary went to the garden' or 'Bernhard is a rhino' or both then John got the apple. Chances are about even that if either 'Bernhard is a rhino' or 'Mary went to the garden' but not both then Lily is a lion.
It is certain that either 'Bernhard is a rhino' or 'John got the apple' but not both.
We doubt that either 'Bernhard is a rhino' or 'John got the apple' but not both.
It is certain that either 'Bernhard is a rhino' or 'John got the apple' 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.
  0.1::factB.
  0.1::factC.
  %hop1
  0.02::factX:-and(factB,factC).
  1.0::factY:-or(factA,factC).
  0.5::factZ:-xor(factC,factA).

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

  query(conclusion).
  
Either 'Bernhard is a rhino' or 'John got the apple' but not both.