Oxford University Press, 1971
Buku Referensi
edited by Thomas M. Paikeday
Holt, Rinehart and Winston, 1976
Buku Referensi
Oxford university press , 1992
Buku Teks
CHalker, Sylvia
Clarendon Press, 1994
Buku Referensi
Wheeler, Marcus
Glarendon Press, 1984
Buku Referensi