There is a very good chance that Julius is a swan. It is certain that Bernhard is a frog. There is almost no chance that Fred is in the school. There is a better than even chance that if either 'Julius is a swan' or 'Fred is in the school' but not both then Daniel dropped the apple. There is a better than even chance that if either 'Fred is in the school' or 'Bernhard is a frog' but not both then Brian is a lion. There is little chance that if 'Fred is in the school' or 'Bernhard is a frog' or both then Sandra left the milk.
There is almost no chance that either 'Julius is a swan' or 'Sandra left the milk' but not both.
We believe that either 'Julius is a swan' or 'Sandra left the milk' but not both.
There is almost no chance that either 'Julius is a swan' or 'Sandra left 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
  0.8::factA.
  1.0::factB.
  0.02::factC.
  %hop1
  0.6::factX:-xor(factA,factC).
  0.6::factY:-xor(factC,factB).
  0.1::factZ:-or(factC,factB).

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

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