CREATE TRIGGER "rtree_<t>_<c>_update4" AFTER UPDATE ON "<t>"
  WHEN OLD."<i>" != NEW."<i>" AND
       (NEW."<c>" ISNULL OR ST_IsEmpty(NEW."<c>"))
BEGIN
  DELETE FROM "rtree_<t>_<c>" WHERE id IN (OLD."<i>", NEW."<i>");
END;