In the ninth century the first Talmudic dictionary ‏‎ערוך‎‏ was written by Zemah Gaon. His work has not come down to us, but most of it was incorporated in the Talmudic dictionary of the same name, written by Nathan of Rome in the eleventh century. The title has also been retained by subsequent compilers of Talmudic dictionaries, including the Aruch Completum, edited by Alexander Kohut (1878-1892). At the same time Amram Gaon compiled the first liturgy, Seder Rab Amram, and thus is the originator of our present prayer-book. The form in which this compilation has come down to us is not as the original left the hands of its editor, for quite a number of later texts are found in it and its order of services is not exactly identical with any of the rituals in use at present. Still, it is the groundwork of the liturgy of Judaism to-day all over the world. From the same period dates, probably, the first Kabalistic book which we possess, the “Sefer Yezirah” (Book of Creation). It may be called a theosophical treatise, written in the language and form of the Mishnah, and based on the philosophy of the Pythagorean and Alexandrian schools. Its subject-matter naturally makes it obscure; from the tenth century at least it has been commented upon. Legend has ascribed its authorship to Rabbi Akiba, and even to Biblical persons such as Abraham. In the ninth century we meet the first traces of a scientific literature. Prominent here is Saadya Gaon (892-942), born in Fayum, and called to Sura as Gaon, quite an unusual event. His literary activity extends over the whole field of Jewish literature. He wrote commentaries on the Bible besides an Arabic translation, and on Talmudic topics. He also composed religious hymns, but the most important of all his works is his ‏‎אמונות ודעות‎‏ (Dogma and Science), the first attempt at a scientific apology for Judaism from a philosophical point of view. His independence brought him into conflict with the Exilarch David ben Zakkai, to whose dictates he would not submit in a matter which he regarded as unjust; consequently he was deposed. Saadya contended that this act was illegal and excommunicated the Exilarch. The latter proved stronger and Saadya was forced into exile. Later on, however, they became reconciled, and Saadya was reinstated (934).