Chances are about even that Greg is a swan. There is little chance that Brian is yellow. It is probably not the case that Mary got the milk. There is a better than even chance that if 'Mary got the milk' or 'Greg is a swan' or both then Winona is a wolf. We doubt that if either 'Mary got the milk' or 'Brian is yellow' but not both then Bernhard is a frog. It is probably the case that if either 'Brian is yellow' or 'Greg is a swan' but not both then John moved to the garden.
We doubt that either 'John moved to the garden' or 'Greg is a swan' but not both.
We doubt that either 'John moved to the garden' or 'Greg is a swan' but not both.
We believe that either 'John moved to the garden' or 'Greg is a swan' 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
  0.5::factA.
  0.1::factB.
  0.25::factC.
  %hop1
  0.6::factX:-or(factC,factA).
  0.2::factY:-xor(factC,factB).
  0.7::factZ:-xor(factB,factA).

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

  query(conclusion).
  
Either 'John moved to the garden' or 'Greg is a swan' but not both.