Votaw, Dow
Prentice-Hall, 1973
Buku Teks
Hamilton, Robert W.
West Publishing, 1992
Buku Teks
Sethi, S. Prakash
Prentice-Hall, 1974
Buku Teks
Dow, Hume
Oxford University Press, 1971
Buku Teks SO
Henn, Harry, Alexander, John R
St.Paul,Minn : West publishing Co, 1983,
Buku Referensi