All three were also involved in a major intellectual project established by the îl-Khânid rulers in 1259: the Maragha Observatory. Tûsî had been given the task by the Mongols of setting up an astronomical observatory, and he asked Kâtibî (among others) to help him. At some stage in the early years of the observatory, Abharî joined them. We know that Kâtibî was teaching both Râzî's Compendium and Khûnajî's Disclosure to students during this period, and that Abharî and Tûsî were debating how best to deal with the challenges raised by Khûnajî to Avicenna's logic. Kâtibî's major works on logic (a long treatise, Summa of Subtle Points, and the textbook, the Shamsiyya) were written after these discussions, and used many of the arguments raised in them. Kâtibî's Shamsiyya was commented on by Qutbaddîn at-Tahtânî (d. 1365), among many others (for details about these other commentaries, see Schmidtke 1991, 2013; Wisnovsky 2004). Tahtânî's commentary records a great many of the technical debates going on among the scholars at the Maragha observatory. Kâtibî's textbook and Tahtânî's commentary together constitute the impressive preparation most Muslim scholars underwent in logic. 