It is probably the case that John moved to the office. Chances are about even that Gertrude is a mouse. It is impossible that Lily is a swan. There is almost no chance that if 'Gertrude is a mouse and John moved to the office' then Bernhard is a lion. It is impossible that if 'Gertrude is a mouse and Lily is a swan' then Antoine is bored. It is highly unlikely that if either 'Gertrude is a mouse' or 'John moved to the office' but not both then Mary grabbed the milk.
It is certain that either 'Mary grabbed the milk' or 'Bernhard is a lion' but not both.
There is almost no chance that either 'Mary grabbed the milk' or 'Bernhard is a lion' but not both.
It is certain that either 'Mary grabbed the milk' or 'Bernhard is a lion' 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
  0.7::factA.
  0.5::factB.
  0.0::factC.
  %hop1
  0.02::factX:-and(factB,factA).
  0.0::factY:-and(factB,factC).
  0.05::factZ:-xor(factB,factA).

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

  query(conclusion).
  
Either 'Mary grabbed the milk' or 'Bernhard is a lion' but not both.