It is probably not the case that Brian is a swan. Chances are about even that Mary went to the kitchen. It is likely that Bernhard is a lion. We doubt that if 'Mary went to the kitchen and Brian is a swan' then Jason is tired. It is probably the case that if 'Bernhard is a lion' or 'Brian is a swan' or both then John moved to the garden. It is probably the case that if 'Brian is a swan' or 'Mary went to the kitchen' or both then Greg is gray.
There is a very good chance that either 'Brian is a swan' or 'Greg is gray' but not both.
It is probably not the case that either 'Brian is a swan' or 'Greg is gray' but not both.
There is a very good chance that either 'Brian is a swan' 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
  0.25::factA.
  0.5::factB.
  0.7::factC.
  %hop1
  0.2::factX:-and(factB,factA).
  0.7::factY:-or(factC,factA).
  0.7::factZ:-or(factA,factB).

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

  query(conclusion).
  
Either 'Brian is a swan' or 'Greg is gray' but not both.