What country did Gil play against on 21–23 september 2007?
CREATE TABLE "doubles_17" (
  "edition" text,
  "round" text,
  "date" text,
  "partnering" text,
  "against" text,
  "surface" text,
  "opponents" text,
  "w_l" text,
  "result" text
);
SELECT "against" FROM "doubles_17" WHERE "date"='21–23 September 2007';