945?-1020?

Persian mathematician and astrologer who considered a number of challenging geometric problems. Notable among his works is Book of the Measurement of Spheres by Spheres, in which he presented 12 theorems involving a large sphere containing between one and three smaller spheres. Some historians maintain than in this work al-Sijzi approached the idea of a four-dimensional sphere, though it is likely that this is the result of his own misunderstanding of the factors he was considering. He did, however, approach the topic suggested in the title of another work, Treatise on How to Imagine the Two Lines Which Approach but Do Not Meet When They Are Produced Indefinitely.