Harrison, Allan
Prentice-Hall, 1992.
Buku Teks
Holden, Nigel J.
Prentice-Hall, 2002
Buku Teks
Lembaga Penelitian Universitas Indonesia, 2003
Artikel Jurnal
Mughaneswari ap Sahadevan
Universiti Utara Malaysia, 2014
Artikel Jurnal
Sojak, Radoslaw
Internationaler Verlag der Wissenschaften, 2018
Buku Teks SO