Chances are slight that Daniel dropped the apple. It is improbable that Mary left the football. We believe that Brian is a swan. There is a better than even chance that if 'Mary left the football and Brian is a swan' then Julius is a lion. It is certain that if either 'Daniel dropped the apple' or 'Brian is a swan' but not both then Bernhard is green. It is likely that if either 'Brian is a swan' or 'Mary left the football' but not both then John got the milk.
There is a very good chance that either 'Brian is a swan' or 'John got the milk' but not both.
It is probably not the case that either 'Brian is a swan' or 'John got the milk' but not both.
There is a very good chance that either 'Brian is a swan' or 'John 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
  0.1::factA.
  0.1::factB.
  0.75::factC.
  %hop1
  0.6::factX:-and(factB,factC).
  1.0::factY:-xor(factA,factC).
  0.7::factZ:-xor(factC,factB).

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

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