CREATE TABLE table_6665 ("Season" TEXT, "Competition" TEXT, "Round" TEXT, "Club" TEXT, "Score" TEXT)

Which competition features the 1st round of Club Union Luxembourg?
SELECT "Competition" FROM table_6665 WHERE "Round" = '1st round' AND "Club" = 'union luxembourg'
SELECT "Competition" FROM "table_6665" WHERE "Club" = 'union luxembourg' AND "Round" = '1st round'