It is probably the case that Gertrude is a wolf. It is certain that Greg is white. It is probably the case that Brian is a rhino. It is almost certain that if either 'Brian is a rhino' or 'Greg is white' but not both then Sandra left the milk. It is probably not the case that if either 'Brian is a rhino' or 'Greg is white' but not both then Julius is green. Chances are about even that if 'Greg is white' or 'Brian is a rhino' or both then Daniel took the milk.
It is probably not the case that either 'Greg is white' or 'Brian is a rhino' but not both.
It is probably not the case that either 'Greg is white' or 'Brian is a rhino' but not both.
We believe that either 'Greg is white' or 'Brian is a rhino' 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
  0.7::factA.
  1.0::factB.
  0.7::factC.
  %hop1
  0.95::factX:-xor(factC,factB).
  0.25::factY:-xor(factC,factB).
  0.5::factZ:-or(factB,factC).

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

  query(conclusion).
  
Either 'Greg is white' or 'Brian is a rhino' but not both.