Leach, E. R., author
Beacon Press, 1970
Buku Teks
Nannes, Caspar H,
The Catholic University, 1960
Buku Teks
Huntington, Samuel P., author
The Belknap Press, 1981
Buku Teks
Karp, Walter, author
Harper & Row, 1979
Buku Teks
Edward, David V.
Prentice-Hall, 1982
Buku Teks