It is highly unlikely that Sandra got the milk. We believe that Brian is white. It is probable that Lily is a swan. Chances are about even that if 'Brian is white' or 'Sandra got the milk' or both then Jason is tired. There is a better than even chance that if 'Sandra got the milk and Brian is white' then Mary went to the bedroom. It is certain that if either 'Lily is a swan' or 'Sandra got the milk' but not both then Bernhard is a rhino.
It is unlikely that either 'Lily is a swan' or 'Sandra got the milk' but not both.
It is likely that either 'Lily is a swan' or 'Sandra got the milk' but not both.
It is unlikely that either 'Lily is a swan' or 'Sandra got the milk' 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
  0.05::factA.
  0.75::factB.
  0.7::factC.
  %hop1
  0.5::factX:-or(factB,factA).
  0.6::factY:-and(factA,factB).
  1.0::factZ:-xor(factC,factA).

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

  query(conclusion).
  
Either 'Lily is a swan' or 'Sandra got the milk' but not both.