It is highly unlikely that Bernhard is a swan. It is highly unlikely that Emily is a sheep. There is a very good chance that John put down the apple. It is certain that if 'Bernhard is a swan and Emily is a sheep' then Brian is a rhino. There is a very good chance that if 'Emily is a sheep and Bernhard is a swan' then Julius is a frog. It is unlikely that if 'Bernhard is a swan' or 'John put down the apple' or both then Mary went to the office.
We doubt that either 'Mary went to the office' or 'Brian is a rhino' but not both.
We doubt that either 'Mary went to the office' or 'Brian is a rhino' but not both.
It is highly likely that either 'Mary went to the office' or 'Brian is a rhino' 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
  0.05::factA.
  0.05::factB.
  0.8::factC.
  %hop1
  1.0::factX:-and(factA,factB).
  0.8::factY:-and(factB,factA).
  0.2::factZ:-or(factA,factC).

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

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