Tài liệu tham khảo WikiPedia: Tukchang http://nk.joins.com/map/i054.htm http://www1.korea-np.co.jp/pk/087th_issue/99032502... http://www.hrnk.org/download/The_Hidden_Gulag.pdf http://unstats.un.org/unsd/demographic/sources/cen...