 In Western European Slavic studies relevant to the research of the dialect is the book by André Mazon about the Slavic songs and the dialects from southwestern Macedonia, published in 1923.The first complete dictionary of the Kostur dialect was published by Blagoy Shklifov.Afterwards, Shklifov analyzed his native Kostur dialect, comparing it and standard Bulgarian with Old Church Slavonic, and explained the development of many sounds in Bulgarian language, notably ѫ.