Matthews, Donald R.
The University of North Carolina Press, 1960
Buku Teks
Westview Press, 1982
Buku Teks
Murray, John Edward, author
Michie, 1990
Buku Teks
Knauth, Oliver D.
Nasional Planning Association, 1960
Buku Teks
Warntz, William
University of Pennsylvania Press , 1959
Buku Teks