CREATE TABLE table_204_549 (id DECIMAL, "series\ number" TEXT, "key" TEXT, "composed" TEXT, "published" TEXT, "opus no." TEXT, "brown" TEXT, "kobylanska" TEXT, "chominski" TEXT, "dedication" TEXT, "notes" TEXT)

which is older , 10-13 or 18-21 ?
SELECT "series\nnumber" FROM table_204_549 WHERE "series\nnumber" IN ('10-13', '18-21') ORDER BY "composed" LIMIT 1
SELECT "series\nnumber" FROM "table_204_549" WHERE "series\nnumber" IN ('10-13', '18-21') ORDER BY "composed" NULLS FIRST LIMIT 1