It is probably not the case that John went to the hallway. We doubt that Winona is a sheep. It is highly likely that Fred left the apple. There is little chance that if 'Fred left the apple and John went to the hallway' then Lily is a lion. It is improbable that if 'Winona is a sheep and Fred left the apple' then Brian is a swan. Chances are slight that if 'Fred left the apple and Winona is a sheep' then Greg is a rhino.
It is unlikely that either 'Winona is a sheep' or 'Brian is a swan' but not both.
It is unlikely that either 'Winona is a sheep' or 'Brian is a swan' but not both.
It is almost certain that either 'Winona is a sheep' or 'Brian is a swan' 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.
  0.2::factB.
  0.9::factC.
  %hop1
  0.1::factX:-and(factC,factA).
  0.1::factY:-and(factB,factC).
  0.1::factZ:-and(factC,factB).

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

  query(conclusion).
  
Either 'Winona is a sheep' or 'Brian is a swan' but not both.