Select Publishing , 2003
Buku Teks
Butwell, Richard
Frederick A. Praeger, 1962
Buku Teks
Butwell, Richard
Praeger Publishers, 1969
Buku Teks
Butwell, Richard
Praeger, 1961
Buku Teks
editors, Robert E. Ward and Roy C. Macridis
Prentice-Hall, 1963
Buku Teks