Witt, Elder
Congressional Quarterly, Inc., 1986
Buku Teks
Findlay, Bruce Allyn, author
Stanford University Press, 1952
Buku Teks
Findlay, Bruce Allyn, author
Stanford University Press, 1959
Buku Teks
Sorauf
Little, Brown and Company, 1980
Buku Teks
Burns, James McGregor, author
Prentice-Hall, 1963
Buku Teks