Ahmad bin Rajab bin Taibugha al-Majdë al-alaâÂÂi bin Abdullah ShihÃÂb alâÂÂDën Abu al-Abbas (; 1359âÂÂ1447 CE) was an Egyptian mathematician and astronomer. His most important mathematical work was "Book of Substance", a voluminous commentary on the Summary of the Operations of Calculations by Ibn al-Banna'.