1. Извори - Primary Sources
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3. Beševliev V., Părvobălgarskite nadpisi, Sofija 19922.
4. Catalogue of Byzantine Seals at Dumbarton Oaks and in the Fogg Museum of Art I, edd. J. Nesbitt - N. Oikonomides, Washington 1991.
5. Concilium Constantinopolitanum A. 691/2 in Trullo Habitum (Concilium Quinisextum), ed. H. Ohme, Acta conciliorum oecumenicorum, II.2.4, Berlin-Boston 2013.