It is probably not the case that John went to the bedroom. It is certain that Sandra took the milk. We believe that Lily is a lion. Chances are about even that if 'John went to the bedroom' or 'Lily is a lion' or both then Jessica is a cat. It is improbable that if 'Sandra took the milk and Lily is a lion' then Winona is a sheep. Chances are about even that if 'Sandra took the milk' or 'Lily is a lion' or both then Mary dropped the apple.
Chances are about even that either 'Winona is a sheep' or 'Jessica is a cat' but not both.
Chances are about even that either 'Winona is a sheep' or 'Jessica is a cat' but not both.
It is highly unlikely that either 'Winona is a sheep' or 'Jessica is a cat' 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.
  1.0::factB.
  0.75::factC.
  %hop1
  0.5::factX:-or(factA,factC).
  0.1::factY:-and(factB,factC).
  0.5::factZ:-or(factB,factC).

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

  query(conclusion).
  
Either 'Winona is a sheep' or 'Jessica is a cat' but not both.