It is improbable that John dropped the apple. We believe that Greg is a rhino. There is a better than even chance that Jeff left the football. It is probably the case that if 'John dropped the apple' or 'Greg is a rhino' or both then Emily is a cat. Chances are about even that if either 'Jeff left the football' or 'Greg is a rhino' but not both then Julius is white. It is highly likely that if either 'Greg is a rhino' or 'Jeff left the football' but not both then Mary got the football.
Chances are slight that either 'Julius is white' or 'Jeff left the football' but not both.
It is probably the case that either 'Julius is white' or 'Jeff left the football' but not both.
Chances are slight that either 'Julius is white' or 'Jeff left the football' 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
  0.1::factA.
  0.75::factB.
  0.6::factC.
  %hop1
  0.7::factX:-or(factA,factB).
  0.5::factY:-xor(factC,factB).
  0.9::factZ:-xor(factB,factC).

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

  query(conclusion).
  
Either 'Julius is white' or 'Jeff left the football' but not both.