Sihombing, Tumpal M.
Fakultas Ekonomi dan Bisnis Universitas Indonesia, 2009
UI - Tesis Open
Mehta, J.K.
Caitanya Publishing House, 1967
Buku Teks
Burns, Arthur Edward
Harcourt, Brace, 1948
Buku Teks
Chang, Semoon
Allyn and Bacon, 1990
Buku Teks SO
Hogendorn, Jan S.
Prentice-Hall, 1995
Buku Teks SO