It is improbable that Lily is yellow. It is highly unlikely that Jeff went to the garden. It is probable that Julius is a lion. Chances are about even that if 'Jeff went to the garden and Julius is a lion' then Gertrude is a wolf. There is a very good chance that if either 'Jeff went to the garden' or 'Julius is a lion' but not both then Greg is a swan. There is almost no chance that if 'Julius is a lion' or 'Lily is yellow' or both then Mary picked up the apple.
There is a better than even chance that either 'Greg is a swan' or 'Jeff went to the garden' but not both.
There is a better than even chance that either 'Greg is a swan' or 'Jeff went to the garden' but not both.
It is highly unlikely that either 'Greg is a swan' or 'Jeff went to the garden' 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.
  0.05::factB.
  0.7::factC.
  %hop1
  0.5::factX:-and(factB,factC).
  0.8::factY:-xor(factB,factC).
  0.02::factZ:-or(factC,factA).

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

  query(conclusion).
  
Either 'Greg is a swan' or 'Jeff went to the garden' but not both.