||Sefer ha-Ittur, a compilation of the main halakhic laws which are of practical application. Part one deals with the various laws of bills, both financial and of divorce. It is arranged according to subject matter but following a mnemonic acrostic Tashkef be-Geza Hokhmah ("Consider the Root of Wisdom"), each letter representing a certain concept. Thus T stands for tenai ("condition"). S for shover ("receipt"). c for kiyyum ("authentication"), etc. Part two includes the laws for the preparation of meat, shehitah, circumcision, tefillin, marriage benedictions, zizit and a separate section entitled "Ten Commandments" containing ten positive commands which must be performed at specific times. This arrangement is unique in halakhic literature. R. Isaac b. Abba Mari made use of his vast knowledge of geonic literature and his work is still an important source for that literature. He also made extensive use of Spanish authorities and those of Germany and northern France. He used the Jerusalem Talmud to a considerable extent and also engaged in establishing the correct text of the Talmud on the basis of ancient sources, some of which are no longer extant.
R. Isaac b. Abba Mari of Marseilles (1120?–1190?), rabbinical scholar in Provence and Spain. He studied under his father, R. Abba Mari b. Isaac, and when only 17 years of age composed a work on the laws of shehitah and forbidden foods, at his father's behest. Later he went to Barcelona, where he was received with great honor and, at the request of R. Sheshet Benveniste, wrote a commentary on chapter 4 of the tractate Menahot which deals with the laws concerning zizit, mezuzah, and tefillin. He corresponded with the most illustrious figures of his generation, such as R. Abraham b. David of Posquieres and R. Jacob Tam, whom he frequently mentions and quotes.