G. Šemkov, „Kirilometodievistika simpozium. Vtori meždunaroden kongres po bălgaristika, Sofija, 23 maj - 3 juni 1986 g.; Hoffer, Angelika, Edle von Sulmtal - Michail Margaritov: Za Kiril i Metodij. An Attempt to Establish the Nationality of the Slav Apostles Constantine and Methodius and an Explanation of Some Circumstances Related to This Question“, SOF, Bd. 1, Nr. 1, S. 380–381, Nov. 2021.