ABSTRACT
The second treatise is entitled Discourse of al-Shaykh Abº ‘Alî alÎasan ibn al-Îasan ibn al-Haytham, renowned for his ‘astounding’ work on the Arithmetic of Transactions, and is very different. It comes down to us in two manuscripts; Istanbul, ‘Atif 1714/13, fols 116r-125r and Berlin Oct. 2970/17 fols 117r-186r. There is doubt over the term ‘al-gharîb’ – meaning ‘astounding’. Al-Îasan ibn al-Haytham was not in the habit of using such expressions to describe his works (and this can be proved). On the other hand, this word can be read as ‘al-qarîb’ which means ‘near’ or ‘easy’. Moreover, the colophon reads: Tamma al-kitæb fî Ìisæb almu‘æmalæt (The Book on the Arithmetic of Transactions is completed…’) without any mention of ‘astounding’. And it is this exact title which appears on the two lists of al-Îasan and of MuÌammad. The book itself deals with ‘the fundamentals of this art’, that is the non-demonstrative study of the operations of this arithmetic: proportion, multiplication, division, addition of fractions. The way the text is presented, it could well be the work of alÎasan ibn al-Haytham, but without supporting evidence, it is impossible to be certain.
