It is unlikely that Bernhard is a swan. It is probably not the case that John went to the garden. It is highly likely that Brian is a rhino. Chances are about even that if 'Bernhard is a swan' or 'Brian is a rhino' or both then Julius is green. We doubt that if 'Bernhard is a swan' or 'Brian is a rhino' or both then Mary got the apple. There is little chance that if either 'John went to the garden' or 'Brian is a rhino' but not both then Greg is a lion.
It is probably not the case that either 'Bernhard is a swan' or 'Mary got the apple' but not both.
It is probably not the case that either 'Bernhard is a swan' or 'Mary got the apple' but not both.
It is probable that either 'Bernhard is a swan' or 'Mary 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.
  0.25::factB.
  0.9::factC.
  %hop1
  0.5::factX:-or(factA,factC).
  0.2::factY:-or(factA,factC).
  0.1::factZ:-xor(factB,factC).

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

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