Analysis of information sources in references of the Wikipedia article "ซีแมออนที่ 1 แห่งบัลแกเรีย" in Thai language version.
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.
