Letters of professor I. V. Popov from his study trip in 1901–1902 to professor S. I. Smirnov: reconstructing their academic relations - Vyacheslav Yachmenik; Denis Kalashnikov (Vestnik Pravoslavnogo Svâto-Tihonovskogo Gumanitarnogo Universiteta: Seriâ II. Istoriâ, Istoriâ Russkoj Pravoslavnoj Cerkvi, 2023)