It is unlikely that Brian is a rhino. We doubt that Mary discarded the milk. There is little chance that Sandra left the milk. There is a very good chance that if 'Brian is a rhino and Mary discarded the milk' then John picked up the apple. It is certain that if 'Brian is a rhino' or 'Sandra left the milk' or both then Lily is a swan. It is improbable that if 'Mary discarded the milk and Brian is a rhino' then Bernhard is a frog.
We doubt that either 'John picked up the apple' or 'Brian is a rhino' but not both.
We doubt that either 'John picked up the apple' or 'Brian is a rhino' but not both.
It is probably the case that either 'John picked up the apple' 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
  0.2::factA.
  0.2::factB.
  0.1::factC.
  %hop1
  0.8::factX:-and(factA,factB).
  1.0::factY:-or(factA,factC).
  0.1::factZ:-and(factB,factA).

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

  query(conclusion).
  
Either 'John picked up the apple' or 'Brian is a rhino' but not both.