Chances are slight that Greg is yellow. It is likely that Julius is a swan. It is certain that Brian is white. It is certain that if 'Julius is a swan and Greg is yellow' then Sandra left the milk. There is a very good chance that if either 'Greg is yellow' or 'Brian is white' but not both then Lily is a lion. There is a very good chance that if 'Julius is a swan' or 'Greg is yellow' or both then Fred went to the garden.
It is certain that either 'Julius is a swan' or 'Lily is a lion' but not both.
Chances are about even that either 'Julius is a swan' or 'Lily is a lion' but not both.
It is certain that either 'Julius is a swan' or 'Lily is a lion' 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.
  1.0::factC.
  %hop1
  1.0::factX:-and(factB,factA).
  0.8::factY:-xor(factA,factC).
  0.8::factZ:-or(factB,factA).

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

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