Ḥananel (early 11th century) produced running commentaries to various tractates. These commentaries could be read with the text of the Talmud and would help explain the meaning of the text. Another important work is the Sefer ha-Mafteaḥ (Book of the Key) by Nissim Gaon, which contains a preface explaining the different forms of Talmudic argumentation and then explains abbreviated passages in the Talmud by cross-referring to parallel passages where the same thought is expressed in full. Commentaries (ḥiddushim) by Joseph ibn Migash on two tractates, Bava Batra and Shevuot, based on Ḥananel and Alfasi, also survive, as does a compilation by Zechariah Aghmati called Sefer ha-Ner. Using a different style, rabbi Nathan b. Jechiel created a lexicon called the Arukh in the 11th century to help translate difficult words. By far the best-known commentary on the Babylonian Talmud is that of Rashi (Rabbi Solomon ben Isaac, 1040–1105). The commentary is comprehensive, covering almost the entire Talmud. Written as a running commentary, it provides a full explanation of the words and explains the logical structure of each Talmudic passage. It is considered indispensable to students of the Talmud. Although Rashi drew upon all his predecessors, his originality in using the material offered by them was unparalleled. His commentaries, in turn, became the basis of the work of his pupils and successors, who composed a large number of supplementary works that were partly in emendation and partly in explanation of Rashi's, and are known under the title "Tosafot". ("additions" or "supplements"). The Tosafot are collected commentaries by various medieval Ashkenazic rabbis on the Talmud (known as Tosafists or Ba'alei Tosafot). One of the main goals of the Tosafot is to explain and interpret contradictory statements in the Talmud. Unlike Rashi, the Tosafot is not a running commentary, but rather comments on selected matters. Often the explanations of Tosafot differ from those of Rashi. In Yeshiva, the integration of Talmud, Rashi and Tosafot, is considered as the foundation (and prerequisite) for further analysis; this combination is sometimes referred to by the acronym "gefet" ( גפ״ת - Gemara, perush Rashi, Tosafot). Among the founders of the Tosafist school were Rabbi Jacob ben Meir (known as Rabbeinu Tam), who was a grandson of Rashi, and, Rabbenu Tam's nephew, rabbi Isaac ben Samuel. The Tosafot commentaries were collected in different editions in the various schools. The benchmark collection of Tosafot for Northern France was that of