Stafford, J.

New York Harcourt, Brace and Company 1944

 Buku Teks

Roald Otnes, Alfred Asterjadhi, Paolo Casari, Michael Goetz, Thor Husoy, Ivor Nissen, Knut Rimstad, Paul van Walree, Michele Zoezi, editors

[Springer, Springer], 2012

 eBooks

edited by Keith Banister, Andrew Campbell

Grolier International, 1993

 Buku Referensi

Draminska, Alicja

Draminski S.A., 2016

 Buku Referensi

Dromgoole, Sarah

Cambridge University Press, 2013

 Buku Teks SO