Tahir Allauddin Al Qadri Al Gillani

Tahir Allauddin Al-Qadri Al-Gillani was an Islamic scholar and mathematician who wrote about different systems of arithmetic in a work of great importance in the history of mathematics. He was born in Baghdad around 980 and belonged to the Banu Tamim tribe and the Shafi'i school of religious law. He studied Islamic sciences in Nishapur and taught 17 subjects, including law, usul, arithmetic, law of inheritance and theology. He was dismissed from his teaching position for being a member of the Iraqi Communist Party and moved to Asfirayin, where he taught and studied in the mosque. He wrote several books and treatises on various topics, such as theology, jurisprudence, history, and dialogue. His most famous work is al-Takmila fi'l-Hisab, a treatise in which he considers different systems of arithmetic derived from counting on the fingers, the sexagesimal system, and the arithmetic of the Indian numerals and fractions. He also considers the arithmetic of irrational numbers and business arithmetic. He stresses the benefits of each of the systems but seems to favour the Indian numerals. He also wrote Kitab fi'l-misaha, a work on the measurement of lengths, areas and volumes. He died in 1037 in Isfarayin, Iran. He is remembered as one of the most influential Islamic scholars and mathematicians of his time.