Szeftel Marc. The Title of the Muscovite Monarch up to the End of the Seventeenth Century. — P. 59–81; Alef Gustav. The Adoption of the Muscovite Two-Headed Eagle: A Discordant View // Rulers and Nobles in Fifteenth-Century Muscovy. — London: Variorum Reprints, 1983. — Item IX; Ostrowski Donald. Muscovy and the Mongols: Cross-Cultural Influences on the Steppe Frontier, 1304–1589. — Cambridge: Cambridge University Press, 1998. — P. 176–187.