[One of the most emotionally charged topics traditionally handled by batei din is determining who should receive an appointment for a rabbinical post. From the Rivash’s description, it seems that the case he discussed was a particularly crucial and heated case.]

Rabbi Mattityahu began to lead a community in France very effectively and so impressed the king that he gave Rabbi Mattityahu sweeping authority over the French Jewish community. He used this to further the community’s tranquility, intervened with governmental authorities, and created Torah centers that trained new rabbis. The whole community accepted him as the final arbiter on all matters of halacha, justice, and communal affairs. Also, he gave all the semichas in the country. Upon Rabbi Mattityahu’s death, his son Yochanan assumed his father’s responsibilities and was accepted by the general community and the king’s court. After five years, another scholar, Rabbi Yeshaya, had a dispute with Rabbi Yochanan, and the former moved to Germany. He made a strong impression on Germany’s venerable, leading rabbi, Maharam Halevi. Maharam Halevi issued a decree that no one should be allowed to serve as a rabbi in France without Rabbi Yeshaya’s permission, not Rabbi Yochanan’s. [The question was raised to the Rivash whether to heed the Maharam Halevi’s decree. Following are the major points in the Rivash’s "position paper." It does not seem that he was asked to formally adjudicate.]

There are four reasons why Rabbi Yochanan should continue with his authority. The Sifrei learns that not only does inheritance apply to kingdom (Devarim 17:20), but that inheritance applies to any position of authority within the Jewish community. Historically this applied to the Kohen Gadol and the head of the Sanhedrin (see Ketubot 103b), as long as the son was a legitimate replacement of his father in regard to piety.
Secondly, once Rabbi Yochanan became the de facto leader, even if he was not formally appointed, he should not be removed without sufficient cause (see Yerushalmi, Horiyot 3:5). Third, since he was accepted by the people, we apply the rule that one may be elevated in sanctity but not have his sanctity diminished (see the application in the realm of the rabbinate in Berachot 28b). Finally, since the king appointed Rabbi Yochanan, we apply the concept that the law of the land is the law. Although we would not allow a non-Jewish king to force an appointment on the Jewish community, once the community accepted it, the king’s authority is also relevant.