We believe that Mary went to the bedroom. Chances are about even that Julius is a swan. It is certain that Brian is a lion. Chances are about even that if 'Mary went to the bedroom and Julius is a swan' then Sandra left the football. There is a better than even chance that if 'Brian is a lion' or 'Julius is a swan' or both then Greg is white. It is almost certain that if 'Mary went to the bedroom and Julius is a swan' then John dropped the apple.
There is a better than even chance that either 'Brian is a lion' or 'John dropped the apple' but not both.
There is a better than even chance that either 'Brian is a lion' or 'John dropped the apple' but not both.
Chances are slight that either 'Brian is a lion' or 'John dropped 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
  0.75::factA.
  0.5::factB.
  1.0::factC.
  %hop1
  0.5::factX:-and(factA,factB).
  0.6::factY:-or(factC,factB).
  0.95::factZ:-and(factA,factB).

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

  query(conclusion).
  
Either 'Brian is a lion' or 'John dropped the apple' but not both.