Who directed the episodes that aired December 15, 1956? 
CREATE TABLE "season_2_1956_57" (
  "series_num" real,
  "season_num" real,
  "title" text,
  "director" text,
  "writer_s" text,
  "airdate" text
);
SELECT "director" FROM "season_2_1956_57" WHERE "airdate"='December 15, 1956';