Gaskell, David R.
Scripta, 1973
Buku Teks SO
Gaskell, David R.
Taylor & Francis Group, 2008
Buku Teks SO
Gaskell, David R.
Taylor and Francis, 2008
Multimedia
Upadhyaya, G.S.
Pergamon Press, 1977
Buku Teks
Rao, Y.V.C.
Wiley Eastern, 1993
Buku Teks SO