The first 47 are devoted to chronology and astronomy, followed by one chapter each on world history, Islamic history, church history[lower-alpha 4] and the seven ecumenical councils plus later councils accepted by the Copts.[1][2] His work on the chronology of the patriarchs demonstrates his mathematical proficiency and is highly valuable to the historian.[2] This book was highly influential. It was cited extensively by the Coptic historian Jirjīs al-Makīn, and then also by the Muslim historians al-Maḳrīzī and Ibn Khaldūn, although they are apparently reliant on al-Makīn.