To the question of the beginning of Slavic writing

In the great Cyril and Methodius problem, the main question is the question of the beginning of Slavic writing. Many prominent Slavic scholars have written about it: Dobrovsky, Shafarik, Bodiansky, Sreznevsky, Yagich, Shakhmatov, Lavrov, Lamansky, Ogienko, Emil Georgiev, etc. And yet it is still open, there is no unified opinion among scholars on it. While some scholars directly connect the beginning of Slavic writing with the Great Moravian mission of Cyril and Methodius (862-863), other scholars move this beginning a few years earlier, connecting it with 855, indicated by Chernorizets Hrabar. This special question - which year to take as the beginning of Slavic writing - has existed almost since the emergence of Slavic studies as a science. For a long time, it was not written about separately, because in most cases, scholars, when they touched on it in their research, took one position or the other. After the Second World War, in our country, somehow imperceptibly, it became the subject of several larger or smaller studies, such as those conducted by Al. Burmov, M. Genov, Em. Georgiev, K. Kuev, P. Petrov, B. St. Angelov, etc. And here two groups emerged - supporters of