It is highly likely that Bernhard is white. It is certain that John dropped the apple. It is certain that Julius is a lion. It is probably not the case that if 'Julius is a lion' or 'John dropped the apple' or both then Mary went to the office. Chances are slight that if 'Bernhard is white' or 'John dropped the apple' or both then Gertrude is a cat. It is almost certain that if 'John dropped the apple' or 'Julius is a lion' or both then Brian is a swan.
It is highly likely that either 'John dropped the apple' or 'Gertrude is a cat' but not both.
It is highly likely that either 'John dropped the apple' or 'Gertrude is a cat' but not both.
It is highly unlikely that either 'John dropped the apple' or 'Gertrude is a cat' 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
  0.9::factA.
  1.0::factB.
  1.0::factC.
  %hop1
  0.25::factX:-or(factC,factB).
  0.1::factY:-or(factA,factB).
  0.95::factZ:-or(factB,factC).

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

  query(conclusion).
  
Either 'John dropped the apple' or 'Gertrude is a cat' but not both.