edited by Norval Morris and David J. Rothman
Oxford University Press, 1995
Buku Teks
Preston, Richard Arthur
Praeger, 1962
Buku Teks
Johnson, Elmer D.
Scarecrow Press, 1970
Buku Teks
Adams, Laurie Schneider
Brown & Benchmark , 1997
Buku Referensi
Jordan, R. Furneaux
Thames, [Date of publication not identified]
Buku Teks SO