Chances are slight that Bernhard is green. We believe that Greg is a lion. It is almost certain that Brian is a swan. It is unlikely that if 'Greg is a lion and Brian is a swan' then Sandra dropped the milk. Chances are about even that if 'Bernhard is green' or 'Greg is a lion' or both then Julius is a rhino. Chances are about even that if 'Greg is a lion' or 'Bernhard is green' or both then John went to the office.
It is highly likely that either 'Brian is a swan' or 'Bernhard is green' but not both.
It is highly likely that either 'Brian is a swan' or 'Bernhard is green' but not both.
It is unlikely that either 'Brian is a swan' or 'Bernhard is green' 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
  0.1::factA.
  0.75::factB.
  0.95::factC.
  %hop1
  0.2::factX:-and(factB,factC).
  0.5::factY:-or(factA,factB).
  0.5::factZ:-or(factB,factA).

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

  query(conclusion).
  
Either 'Brian is a swan' or 'Bernhard is green' but not both.