CREATE TABLE table_204_637 (id DECIMAL, "type" TEXT, "gauge" TEXT, "railway" TEXT, "works no." TEXT, "year" TEXT, "builder" TEXT)

hanomag and franco belge , belgium both built garratts for which railway ?
SELECT "railway" FROM table_204_637 WHERE "builder" = 'franco-belge, belgium'
SELECT "railway" FROM "table_204_637" WHERE "builder" = 'franco-belge, belgium'