We believe that Brian is white. It is unlikely that John moved to the garden. There is a very good chance that Mary went to the office. We doubt that if 'Brian is white and John moved to the garden' then Greg is a swan. It is highly likely that if 'Mary went to the office and John moved to the garden' then Julius is a rhino. It is certain that if 'Mary went to the office' or 'Brian is white' or both then Bernhard is a frog.
It is highly unlikely that either 'Brian is white' or 'Greg is a swan' but not both.
It is probable that either 'Brian is white' or 'Greg is a swan' but not both.
It is highly unlikely that either 'Brian is white' or 'Greg is a swan' 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
  0.75::factA.
  0.2::factB.
  0.8::factC.
  %hop1
  0.2::factX:-and(factA,factB).
  0.9::factY:-and(factC,factB).
  1.0::factZ:-or(factC,factA).

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

  query(conclusion).
  
Either 'Brian is white' or 'Greg is a swan' but not both.