Smith, Rhona K., author
Routledge, 2010
Buku Teks
Holcombe, Arthur N.
New York University press, 1948
Buku Teks
Jay Stewart Publications, Inc., 1971
Buku Teks
United Nations, 1988
Buku Teks
Carey, John, author
Oceana Publications, Inc, 1968
Buku Teks