Chances are slight that Yann is bored. It is unlikely that Greg is gray. It is certain that Daniel got the milk. Chances are about even that if either 'Daniel got the milk' or 'Greg is gray' but not both then John went to the bedroom. We doubt that if 'Daniel got the milk' or 'Greg is gray' or both then Sandra left the apple. There is little chance that if 'Yann is bored' or 'Greg is gray' or both then Jessica is a mouse.
It is highly likely that either 'Yann is bored' or 'Daniel got the milk' but not both.
It is highly likely that either 'Yann is bored' or 'Daniel got the milk' but not both.
It is highly unlikely that either 'Yann is bored' or 'Daniel got the milk' 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
  0.1::factA.
  0.2::factB.
  1.0::factC.
  %hop1
  0.5::factX:-xor(factC,factB).
  0.2::factY:-or(factC,factB).
  0.1::factZ:-or(factA,factB).

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

  query(conclusion).
  
Either 'Yann is bored' or 'Daniel got the milk' but not both.