Speransky M.N. Mystery writing in South Slavic and Russian monuments of writing. In Russian (ask us if in doubt)/Speranskiy M.N. Taynopis' v yugo-slavyanskikh i russkikh pamyatnikakh pis'ma. Encyclopedia of Slavic Philology. Issue 4.3. Publishing House of the Academy of Sciences of the USSR. 1929. 162 p. SKUalbcad5fcbb51e8af5f.