Howarth, David, author
McGraw-Hill, 1966
Buku Teks
Passmore, John, author
Gerald Duckworth, 1957
Buku Teks
Passmore, John, author
Penguin Books, 1972
Buku Teks
Howarth, David, author
Edward Elgar, 2013
Buku Teks
Penniman, T.K.
Duckworth, 1935
Buku Teks