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Andreev, 1999, p. 19. (BG) Ĭordan Andreev, Ivan Lazarov e Plamen Pavlov, Koĭ koĭ e v srednovekovna Bŭlgarii︠a︡, 2ª ed., Sofii︠a︡, Izdatelska kŭshta "Petŭr Beron", 1999, ISBN954-402-047-0, OCLC45621805.
Fine, 1994, p. 141. (EN) John V. A. Fine, The late medieval Balkans : a critical survey from the late twelfth century to the Ottoman Conquest, a cura di Ann Arbor, University of Michigan Press, 1994, ISBN978-0-472-10079-8, OCLC749133662.