It is certain that Mary got the apple. It is probably not the case that Emily is a wolf. Chances are about even that John left the milk. It is unlikely that if either 'Mary got the apple' or 'John left the milk' but not both then Lily is a swan. We doubt that if either 'Emily is a wolf' or 'Mary got the apple' but not both then Julius is a swan. It is probably not the case that if 'Emily is a wolf and Mary got the apple' then Bernhard is a lion.
It is probably not the case that 'Julius is a swan' or 'Lily is a swan' or both.
It is probably not the case that 'Julius is a swan' or 'Lily is a swan' or both.
There is a very good chance that 'Julius is a swan' or 'Lily is a swan' or 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
  1.0::factA.
  0.25::factB.
  0.5::factC.
  %hop1
  0.2::factX:-xor(factA,factC).
  0.2::factY:-xor(factB,factA).
  0.25::factZ:-and(factB,factA).

  %hop2
  conclusion:-or(factY,factX).

  query(conclusion).
  
'Julius is a swan' or 'Lily is a swan' or both.