Artikel Jurnal
Hewitt, James
Wayland, 1979
Buku Teks SO
edited by Gabriele vom Bruck and Barbara Bodenhorn
Cambridge University Press, 2006
Buku Teks SO
Schmadel, Lutz D.
Springer, 2012
eBooks
Plowden, C. Chicheley
George Allen and Unwin, 1972
Buku Teks SO