Chances are about even that Brian is a swan. It is highly unlikely that Julius is white. Chances are about even that Sandra left the apple. It is likely that if 'Sandra left the apple and Julius is white' then Lily is gray. Chances are slight that if 'Julius is white and Sandra left the apple' then Bernhard is a rhino. There is a very good chance that if 'Sandra left the apple and Brian is a swan' then John moved to the garden.
Chances are about even that either 'Julius is white' or 'Brian is a swan' but not both.
Chances are about even that either 'Julius is white' or 'Brian is a swan' but not both.
There is almost no chance that either 'Julius is white' or 'Brian 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.
  0.05::factB.
  0.5::factC.
  %hop1
  0.7::factX:-and(factC,factB).
  0.1::factY:-and(factB,factC).
  0.8::factZ:-and(factC,factA).

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

  query(conclusion).
  
Either 'Julius is white' or 'Brian is a swan' but not both.