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 - Šemkov, Georgi (Südost-Forschungen, 2021)