He compiled an _Aruch_, or Talmudical Lexicon.

Of the most active of the Gaonim, Saadiah, more will be said in a subsequent chapter.

We will now pass on to Sherira, who in 987 wrote his famous "Letter," containing a history of the Jewish Tradition, a work which stamps the author as at once learned and critical.

It shows that the Gaonim were not afraid nor incapable of facing such problems as this: Was the Mishnah _orally_ transmitted to the Amoraim (or Rabbis of the Talmud), or was it _written down_ by the compiler?
Sherira accepted the former alternative.
The latest Gaonim were far more productive than the earlier.

Samuel, the son of Chofni, who died in 1034, and the last of the Gaonim, Hai, who flourished from 998 to 1038, were the authors of many works on the Talmud, the Bible, and other branches of Jewish literature.