It is probable that Brian is green. We doubt that Gertrude is a mouse. It is improbable that John discarded the apple. It is highly unlikely that if 'John discarded the apple' or 'Brian is green' or both then Julius is a swan. It is likely that if either 'John discarded the apple' or 'Gertrude is a mouse' but not both then Sandra dropped the milk. It is impossible that if either 'John discarded the apple' or 'Brian is green' but not both then Mary moved to the garden.
It is improbable that either 'John discarded the apple' or 'Brian is green' but not both.
It is probably the case that either 'John discarded the apple' or 'Brian is green' but not both.
It is improbable that either 'John discarded the apple' or 'Brian 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
  0.7::factA.
  0.2::factB.
  0.1::factC.
  %hop1
  0.05::factX:-or(factC,factA).
  0.7::factY:-xor(factC,factB).
  0.0::factZ:-xor(factC,factA).

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

  query(conclusion).
  
Either 'John discarded the apple' or 'Brian is green' but not both.