Rivash is Rabbi Yitzchak bar Sheshet, he was around the year 5134, see his responsum 385, from the city of Aliyero and there he is buried, and he was from the Profiano family. Rabbi Peretz Kohen was his teacher as is evident from his book section 27, and Rabbi Nissim was his teacher, and in section 269 it is evident that he wrote to Rabbi Chasdai Kaskash [(see above year 5140) Shomer HaDat, letter 61...

Rabbi Menachem ben Zerach ben the holy Rabbeinu Aharon from France authored Sefer Tzeda LeDerekh in honor of Don Shmuel Abravanel [(see above year 5300)] whose name was added at the time of the destruction of Van de Sheglia, and this Rabbi Menachem was a student of Rabbi Yehudah son of the Rosh and passed away in Tulitila in the year 5134, and he was also a student of Rabbi Yehoshua who authored...

Rabbeinu Yosef bar Tuvyah called Rivat, and I received that his name was Rabbi Yosef Tov Elem, was in this generation and he was the teacher of Migdal Oz [(Shomer HaDat, letter 58)]: