It is impossible that Brian is white. It is highly likely that Mary grabbed the milk. We doubt that Lily is a rhino. It is likely that if 'Brian is white and Lily is a rhino' then Sandra dropped the milk. Chances are about even that if 'Lily is a rhino' or 'Brian is white' or both then John discarded the apple. It is probable that if 'Lily is a rhino and Mary grabbed the milk' then Bernhard is a swan.
It is likely that either 'Lily is a rhino' or 'Brian is white' but not both.
We doubt that either 'Lily is a rhino' or 'Brian is white' but not both.
It is likely that either 'Lily is a rhino' or 'Brian is white' 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
  0.0::factA.
  0.9::factB.
  0.2::factC.
  %hop1
  0.7::factX:-and(factA,factC).
  0.5::factY:-or(factC,factA).
  0.7::factZ:-and(factC,factB).

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

  query(conclusion).
  
Either 'Lily is a rhino' or 'Brian is white' but not both.