CREATE TABLE table_41618 ("Year" FLOAT, "Division" FLOAT, "League" TEXT, "Regular Season" TEXT, "Playoffs" TEXT, "Open Canada Cup" TEXT)

Which league's playoffs was national semi-finals?
SELECT "League" FROM table_41618 WHERE "Playoffs" = 'national semi-finals'
SELECT "League" FROM "table_41618" WHERE "Playoffs" = 'national semi-finals'