Philips
Chancellor Press, 1999
Buku Referensi
Beckingham, C. F. [Charles Fraser]
Macmillan & Co., 1960
Buku Referensi
Natkiel, Richard
Facts on Eile, 1986
Buku Referensi
Black, Jeremy
Cambridge University Press, 1996
Buku Referensi
Griffiths, Ieuan Ll.
Routledge, 1994
Buku Teks SO