We doubt that Greg is yellow. Chances are about even that Brian is green. It is impossible that Mary went to the hallway. There is little chance that if 'Mary went to the hallway' or 'Greg is yellow' or both then John got the apple. We believe that if 'Mary went to the hallway' or 'Greg is yellow' or both then Bernhard is green. It is highly unlikely that if 'Mary went to the hallway' or 'Brian is green' or both then Julius is a frog.
Chances are slight that either 'Bernhard is green' or 'John got the apple' but not both.
Chances are slight that either 'Bernhard is green' or 'John got the apple' but not both.
It is probable that either 'Bernhard is green' or 'John got the apple' 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.
  0.5::factB.
  0.0::factC.
  %hop1
  0.1::factX:-or(factC,factA).
  0.75::factY:-or(factC,factA).
  0.05::factZ:-or(factC,factB).

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

  query(conclusion).
  
Either 'Bernhard is green' or 'John got the apple' but not both.