It is probably the case that Gertrude is a cat. We doubt that John grabbed the milk. It is unlikely that Julius is a frog. It is likely that if 'Gertrude is a cat' or 'Julius is a frog' or both then Greg is a frog. It is probably not the case that if either 'Gertrude is a cat' or 'John grabbed the milk' but not both then Bernhard is gray. We doubt that if either 'Julius is a frog' or 'Gertrude is a cat' but not both then Mary went to the office.
It is impossible that either 'Mary went to the office' or 'Gertrude is a cat' but not both.
There is a better than even chance that either 'Mary went to the office' or 'Gertrude is a cat' but not both.
It is impossible that either 'Mary went to the office' 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
  0.7::factA.
  0.2::factB.
  0.2::factC.
  %hop1
  0.7::factX:-or(factA,factC).
  0.25::factY:-xor(factA,factB).
  0.2::factZ:-xor(factC,factA).

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

  query(conclusion).
  
Either 'Mary went to the office' or 'Gertrude is a cat' but not both.