Ewing, J.H., editor
Dell Publishing, 1964
Buku Teks SO
edited by John R. Hinnells
Penguin Books, 1985
Buku Referensi
edited by Stewart Sutherland, Leslie Houlden, Peter Clarke, Friedhelm Hardy
Routledge, 1988
Buku Referensi
Gaer, Joseph
Dodd, Mead, 1956
Buku Teks SO
Gaer, Joseph
Dodd, Mead, 1956
Buku Teks SO