Worden, Robert L., ed. (21 April 2011). North Korea: A Country Study. Area Handbook Series (5th ed.). Washington: Government Printing Office. p. 117. ISBN978-0-16-088278-4. Archived from the original on 16 February 2017. Retrieved 10 October 2016.
Worden, Robert L., ed. (21 April 2011). North Korea: A Country Study. Area Handbook Series (5th ed.). Washington: Government Printing Office. p. 117. ISBN978-0-16-088278-4. Archived from the original on 16 February 2017. Retrieved 10 October 2016.