Bookchin, Murray
Black Rose Books, 1991
Buku Teks
Hawley, Amos H., author
The University of Chicago Press, 1986
Buku Teks
Hawley, Amos H., author
The Ronald Press, 1950
Buku Teks
Watson, Richard A., author
Harcourt, Brace and World, 1969
Buku Teks
Zipf, George Kingsley, author
Hafner, 1965
Buku Teks