It is certain that Brian is a frog. It is likely that Bernhard is green. It is probably the case that Lily is green. We doubt that if either 'Brian is a frog' or 'Bernhard is green' but not both then Gertrude is a cat. It is unlikely that if 'Bernhard is green' or 'Lily is green' or both then Mary dropped the milk. It is certain that if 'Lily is green' or 'Brian is a frog' or both then John moved to the garden.
There is a very good chance that either 'Brian is a frog' or 'Lily is green' but not both.
It is probably not the case that either 'Brian is a frog' or 'Lily is green' but not both.
There is a very good chance that either 'Brian is a frog' or 'Lily is green' 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
  1.0::factA.
  0.7::factB.
  0.7::factC.
  %hop1
  0.2::factX:-xor(factA,factB).
  0.2::factY:-or(factB,factC).
  1.0::factZ:-or(factC,factA).

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

  query(conclusion).
  
Either 'Brian is a frog' or 'Lily is green' but not both.