It is impossible that Julius is a frog. It is certain that Fred went to the garden. There is a very good chance that Lily is gray. There is a better than even chance that if 'Fred went to the garden' or 'Lily is gray' or both then Brian is yellow. There is a very good chance that if either 'Fred went to the garden' or 'Julius is a frog' but not both then Greg is a swan. There is a better than even chance that if 'Fred went to the garden' or 'Julius is a frog' or both then Mary put down the apple.
It is improbable that either 'Fred went to the garden' or 'Julius is a frog' but not both.
It is certain that either 'Fred went to the garden' or 'Julius is a frog' but not both.
It is improbable that either 'Fred 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
  0.0::factA.
  1.0::factB.
  0.8::factC.
  %hop1
  0.6::factX:-or(factB,factC).
  0.8::factY:-xor(factB,factA).
  0.6::factZ:-or(factB,factA).

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

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