Isaac ibn al-Ahdab


Itzḥak ben Shlomo ibn al-Aḥdab ben Tzaddiq ha-Sefardi was a Jewish mathematician, astronomer, and poet.
Ibn al-Aḥdab was born in Castile to a prominent Jewish family. He was a student of Judah ben Asher II, the great-grandson of Asher ben Yeḥiel of Cologne, who was killed in the anti-Jewish massacres of 1391. By 1396 Ibn al-Aḥdab had fled Spain and was in Sicily, where he lived until his death around 1426.

Work

He studied the algebra of Maghrebi mathematician Ibn al-Bannā and published The Epistle of the Number, a translation and detailed commentary on Ibn al-Bannā's 13th century treatise Talḵīṣ ʿAmal al-Ḥisāb. The work is notable in being the first known Hebrew-language treatise to include extensive algebraic theories and operations.
His main astronomical work was Oraḥ selulah, a set of tables in Hebrew for conjunctions and oppositions of the Sun and the Moon.