Chances are about even that John took the apple. There is almost no chance that Lily is a swan. It is likely that Mary moved to the office. It is highly unlikely that if 'Mary moved to the office and Lily is a swan' then Julius is a frog. It is likely that if 'Lily is a swan and John took the apple' then Jeff went to the garden. It is improbable that if either 'Lily is a swan' or 'John took the apple' but not both then Brian is a rhino.
It is highly likely that either 'Jeff went to the garden' or 'Julius is a frog' but not both.
It is impossible that either 'Jeff went to the garden' or 'Julius is a frog' but not both.
It is highly likely that either 'Jeff went to the garden' or 'Julius is a frog' 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.
  0.02::factB.
  0.7::factC.
  %hop1
  0.05::factX:-and(factC,factB).
  0.7::factY:-and(factB,factA).
  0.1::factZ:-xor(factB,factA).

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

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