Who was the writer who wrote the episode that was aired on September 11, 1972?
CREATE TABLE "season_18_1972_73" (
  "series_num" real,
  "season_num" real,
  "title" text,
  "director" text,
  "writer_s" text,
  "airdate" text
);
SELECT "writer_s" FROM "season_18_1972_73" WHERE "airdate"='September 11, 1972';