Delightful book, an absolute gem. El-Said's writing is economical, crystaline and accesible.
He explains how all manner of repeated patterns used in Islamic art are created, from 1st principals up. You need NO prior knowledge of geometry, maths or anything much else to use this. That said if you do have some knowledge of maths, you'll get more out of it, as he does explore how the forms work, as well as simply describing their construction.
Beautifully printed in oceans of blank page, this is a book to wallow in. Clear diagrams and words reflect an ordered mind.