There is little chance that Lily is a swan. It is certain that Mary went to the bedroom. It is probably not the case that Greg is a frog. There is a better than even chance that if 'Greg is a frog' or 'Lily is a swan' or both then Bernhard is white. It is unlikely that if either 'Mary went to the bedroom' or 'Greg is a frog' but not both then Sandra left the football. There is a better than even chance that if 'Mary went to the bedroom and Lily is a swan' then John got the milk.
We believe that either 'Sandra left the football' or 'Lily is a swan' but not both.
We doubt that either 'Sandra left the football' or 'Lily is a swan' but not both.
We believe that either 'Sandra left the football' or 'Lily 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
  0.1::factA.
  1.0::factB.
  0.25::factC.
  %hop1
  0.6::factX:-or(factC,factA).
  0.2::factY:-xor(factB,factC).
  0.6::factZ:-and(factB,factA).

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

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