CREATE TABLE table_62013 ("Outcome" TEXT, "Edition" FLOAT, "Round" TEXT, "Opponent Team" TEXT, "Surface" TEXT, "Opponent" TEXT, "Score" TEXT)

What is Opponent, when Round is World Group?
SELECT "Opponent" FROM table_62013 WHERE "Round" = 'world group'
SELECT "Opponent" FROM "table_62013" WHERE "Round" = 'world group'