Dvornik, Francis. The Slavs: Their Early History and Civilization. Boston, American Academy of Arts and Sciences, 1956. с. 179. The Psalter and the Book of Prophets were adapted or „modernized“ with special regard to their use in Bulgarian churches, and it was in this school that glagolitic writing was replaced by the so-called Cyrillic writing, which was more akin to the Greek uncial, simplified matters considerably and is still used by the Orthodox Slavs.
