 Complete the following phrase:  Theoktistos continued the persecution of the Paulicians, which had been initiated by Theodora in 843. Many fled to Arab territory, where with Umar al-Aqtas aid they established a state of their own at Tephrike under their leader Karbeas. Theoktistos concluded a truce with the Abbasid Caliphate and arranged an exchange of prisoners that took place on 16 September 845. Nevertheless, in the same year, the execution of the surviving Byzantine prisoners from the Arab 