It is improbable that Greg is yellow. It is probably the case that Lily is a swan. There is a better than even chance that Julius is white. There is little chance that if 'Lily is a swan' or 'Julius is white' or both then Bernhard is gray. Chances are slight that if 'Lily is a swan and Greg is yellow' then Brian is a frog. It is probably the case that if either 'Greg is yellow' or 'Julius is white' but not both then John took the apple.
It is highly unlikely that either 'Lily is a swan' or 'Julius is white' but not both.
Chances are about even that either 'Lily is a swan' or 'Julius is white' but not both.
It is highly unlikely that either 'Lily is a swan' 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.
  0.7::factB.
  0.6::factC.
  %hop1
  0.1::factX:-or(factB,factC).
  0.1::factY:-and(factB,factA).
  0.7::factZ:-xor(factA,factC).

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

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