It is likely that Greg is a swan. It is probable that Lily is white. It is probably not the case that Brian is a rhino. It is certain that if 'Brian is a rhino' or 'Greg is a swan' or both then Bernhard is a frog. Chances are slight that if either 'Greg is a swan' or 'Brian is a rhino' but not both then John dropped the milk. It is probably the case that if either 'Lily is white' or 'Greg is a swan' but not both then Mary went to the kitchen.
There is almost no chance that either 'Mary went to the kitchen' or 'Brian is a rhino' but not both.
Chances are about even that either 'Mary went to the kitchen' or 'Brian is a rhino' but not both.
There is almost no chance that either 'Mary went to the kitchen' or 'Brian is a rhino' 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
  1.0::factX:-or(factC,factA).
  0.1::factY:-xor(factA,factC).
  0.7::factZ:-xor(factB,factA).

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

  query(conclusion).
  
Either 'Mary went to the kitchen' or 'Brian is a rhino' but not both.