Chances are about even that Greg is green. We doubt that Jeff left the apple. It is certain that Bernhard is a swan. It is highly unlikely that if 'Bernhard is a swan and Jeff left the apple' then Julius is white. There is a better than even chance that if 'Bernhard is a swan and Greg is green' then Mary moved to the office. There is almost no chance that if either 'Jeff left the apple' or 'Bernhard is a swan' but not both then John went to the garden.
It is probably the case that either 'Bernhard is a swan' or 'Mary moved to the office' but not both.
It is probably the case that either 'Bernhard is a swan' or 'Mary moved to the office' but not both.
There is little chance that either 'Bernhard is a swan' or 'Mary moved to the office' 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
  0.5::factA.
  0.2::factB.
  1.0::factC.
  %hop1
  0.05::factX:-and(factC,factB).
  0.6::factY:-and(factC,factA).
  0.02::factZ:-xor(factB,factC).

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

  query(conclusion).
  
Either 'Bernhard is a swan' or 'Mary moved to the office' but not both.