Legge, James, author
[publisher not identified], [date of publication not identified]
Buku Referensi
Courtenay, Bryce, author
Penguin Books, 2001
Buku Teks
Hanks, Gardner C.
Herald Press, 1997
Buku Teks
Spriggs, John, author
Springer, 2012
eBooks
Artikel Jurnal