"O pismeneh" ("On Letters") - the tractate written by Tsrnorizec Hrabar (an unknown author connected with the name of St. Clement and St. Naum) on the way of creation the first Slavic alphabet created by St. Cyril and St. Methodius in the second half of the 9^th century in Macedonia. Transcript from 1348, The Laurentie’s Miscellany