 Complete the following phrase:  Great Moravia briefly regained control over the emerging Bohemian principality upon Bořivojs death in 888890 until, in 895, his son Spytihněv together with the Slavník prince Witizla swore allegiance to the East Frankish king Arnulf of Carinthia in Regensburg. He and his younger brother Vratislaus then ruled over Central Bohemia around Prague. They were able to protect their realm from the Magyar forces which crushed an East Frankish army in the 907 Battle of Pressburg during the 