CREATE TABLE table_4 ("No" FLOAT, "Date" TEXT, "Round" TEXT, "Circuit" TEXT, "Pole Position" TEXT, "Fastest Lap" TEXT, "Race winner" TEXT, "Report" TEXT)

Where was Assen held?
SELECT "Round" FROM table_4 WHERE "Circuit" = 'Assen'
SELECT "Round" FROM "table_4" WHERE "Circuit" = 'Assen'