Šemkov, G. „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“. Südost-Forschungen, Bd. 1, Nr. 1, November 2021, S. 380-1, http://bsb0sit-zepweb01.bsb.lrz.de/portal/index.php/sof/article/view/8324.