It is probably the case that Yann is tired. It is highly likely that Daniel got the football. We doubt that Brian is white. Chances are slight that if either 'Yann is tired' or 'Daniel got the football' but not both then Lily is a swan. It is improbable that if 'Yann is tired and Brian is white' then Jeff dropped the apple. It is likely that if 'Brian is white and Daniel got the football' then Mary went to the bedroom.
It is probably the case that either 'Jeff dropped the apple' or 'Mary went to the bedroom' but not both.
There is little chance that either 'Jeff dropped the apple' or 'Mary went to the bedroom' but not both.
It is probably the case that either 'Jeff dropped the apple' or 'Mary went to the bedroom' 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.
  0.9::factB.
  0.2::factC.
  %hop1
  0.1::factX:-xor(factA,factB).
  0.1::factY:-and(factA,factC).
  0.7::factZ:-and(factC,factB).

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

  query(conclusion).
  
Either 'Jeff dropped the apple' or 'Mary went to the bedroom' but not both.