There is little chance that Julius is white. It is highly likely that Fred put down the apple. It is impossible that Sandra got the milk. It is highly unlikely that if 'Sandra got the milk' or 'Julius is white' or both then Greg is a rhino. Chances are slight that if 'Sandra got the milk' or 'Fred put down the apple' or both then John left the football. We believe that if either 'Fred put down the apple' or 'Julius is white' but not both then Lily is a swan.
It is improbable that either 'Sandra got the milk' or 'Julius is white' but not both.
It is improbable that either 'Sandra got the milk' or 'Julius is white' but not both.
It is likely that either 'Sandra got the milk' or 'Julius is white' 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.
  0.9::factB.
  0.0::factC.
  %hop1
  0.05::factX:-or(factC,factA).
  0.1::factY:-or(factC,factB).
  0.75::factZ:-xor(factB,factA).

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

  query(conclusion).
  
Either 'Sandra got the milk' or 'Julius is white' but not both.