There is a better than even chance that Bernhard is white. It is highly likely that Mary left the football. There is almost no chance that Julius is a swan. It is improbable that if either 'Mary left the football' or 'Bernhard is white' but not both then Daniel grabbed the milk. Chances are slight that if 'Julius is a swan and Bernhard is white' then Brian is a frog. It is unlikely that if 'Julius is a swan and Bernhard is white' then John dropped the apple.
Chances are slight that either 'Bernhard is white' or 'Brian is a frog' but not both.
There is a better than even chance that either 'Bernhard is white' or 'Brian is a frog' but not both.
Chances are slight that either 'Bernhard is white' or 'Brian is a frog' 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
  0.6::factA.
  0.9::factB.
  0.02::factC.
  %hop1
  0.1::factX:-xor(factB,factA).
  0.1::factY:-and(factC,factA).
  0.2::factZ:-and(factC,factA).

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

  query(conclusion).
  
Either 'Bernhard is white' or 'Brian is a frog' but not both.