Document(
 Prefix(ex <http://example.org/example#>)
 Prefix(xs <http://www.w3.org/2001/XMLSchema#>) 

 Group ( 
  Forall ?X (
   If 
      ?X[ex:status -> "normal" ex:discount -> "10"] 
   Then Do ( 
      Retract (?X[ex:discount -> "10")
      Assert  (?X[ex:discount -> "0"])
   )
  )

  ex:john[ex:status -> "normal" ex:discount -> "10"]

 )
)