It is likely that Mary went to the kitchen. It is likely that Greg is gray. It is probably not the case that Lily is a swan. It is probable that if 'Mary went to the kitchen and Lily is a swan' then Brian is green. We believe that if either 'Lily is a swan' or 'Mary went to the kitchen' but not both then Bernhard is a lion. It is probably the case that if either 'Greg is gray' or 'Lily is a swan' but not both then John picked up the apple.
Chances are about even that either 'Mary went to the kitchen' or 'Greg is gray' but not both.
Chances are about even that either 'Mary went to the kitchen' or 'Greg is gray' but not both.
There is almost no chance that either 'Mary went to the kitchen' or 'Greg is gray' 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
  0.7::factA.
  0.7::factB.
  0.25::factC.
  %hop1
  0.7::factX:-and(factA,factC).
  0.75::factY:-xor(factC,factA).
  0.7::factZ:-xor(factB,factC).

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

  query(conclusion).
  
Either 'Mary went to the kitchen' or 'Greg is gray' but not both.