CREATE TABLE table_31259 ("No. in series" FLOAT, "No. in season" FLOAT, "Title" TEXT, "Directed by" TEXT, "Written by" TEXT, "Original air date" TEXT, "Production code" FLOAT)

How many different pairs of writers wrote the episode with series number 56?
SELECT COUNT("Written by") FROM table_31259 WHERE "No. in series" = '56'
SELECT COUNT("Written by") FROM "table_31259" WHERE "No. in series" = '56'