It is certain that Gertrude is a sheep. It is probably the case that Mary dropped the apple. There is almost no chance that Lily is a lion. It is unlikely that if 'Gertrude is a sheep and Mary dropped the apple' then Bernhard is a frog. It is probable that if either 'Lily is a lion' or 'Mary dropped the apple' but not both then Brian is yellow. There is a very good chance that if either 'Lily is a lion' or 'Mary dropped the apple' but not both then John went to the hallway.
There is a better than even chance that either 'Bernhard is a frog' or 'Mary dropped the apple' but not both.
There is a better than even chance that either 'Bernhard is a frog' or 'Mary dropped the apple' but not both.
There is little chance that either 'Bernhard is a frog' or 'Mary dropped the apple' 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
  1.0::factA.
  0.7::factB.
  0.02::factC.
  %hop1
  0.2::factX:-and(factA,factB).
  0.7::factY:-xor(factC,factB).
  0.8::factZ:-xor(factC,factB).

  %hop2
  conclusion:-xor(factX,factB).

  query(conclusion).
  
Either 'Bernhard is a frog' or 'Mary dropped the apple' but not both.