It is certain that Mary went to the garden. There is little chance that Bernhard is a swan. Chances are slight that Lily is yellow. We believe that if 'Bernhard is a swan' or 'Lily is yellow' or both then Winona is a mouse. There is little chance that if either 'Mary went to the garden' or 'Bernhard is a swan' but not both then Brian is green. It is impossible that if 'Bernhard is a swan' or 'Mary went to the garden' or both then John moved to the garden.
It is unlikely that either 'Bernhard is a swan' or 'Brian is green' but not both.
It is unlikely that either 'Bernhard is a swan' or 'Brian is green' but not both.
It is probable that either 'Bernhard is a swan' 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
  1.0::factA.
  0.1::factB.
  0.1::factC.
  %hop1
  0.75::factX:-or(factB,factC).
  0.1::factY:-xor(factA,factB).
  0.0::factZ:-or(factB,factA).

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

  query(conclusion).
  
Either 'Bernhard is a swan' or 'Brian is green' but not both.