London: Transactions of the Philological Society. Volume 53, Issue 1, pages 157–177, November 1954. Grammatical Sketch. - 21 p.
Хеннинг В. Б. Язык Древнего Азербайджана (на англ. яз.)
It is generally agreed, and indeed not subject to serious doubt, that before the advent of the Turks Iranian languages were spoken here in Azerbaijan and Zenjan, as elsewhere in Persia. From the distribution of the Iranian dialects one may infer the group of Iranian to which the lost language of Azerbaijan belonged.