オグール語群
2007.
Johanson, Lars. 2000. "Linguistic convergence in the Volga area." In: Gilbers, Dicky & Nerbonne, John & Jos Schaeken (ed.). Languages in contact. Amsterdam & Atlanta: Rodopi. (Studies in Slavic and General linguistics 28.), pp. 165–178.
Johanson, Lars. 2007. Chuvash. Encyclopedia of Language and Linguistics. Oxford: Elsevier.
Krueger, John. 1961. Chuvash Manual. Bloomington: Indiana University Publications.
Liptak, Pal. 1983. Avars and Ancient Hungarians. Budapest: Akademiai Kiado.
Maenchen-Helfen, Otto J. 1973. The world of the Huns: Studies in their history and culture. Berkeley: University of California Press.
Menges, K. H.