1. As an example of the differences between various editions of al-Ṭūsī’s Taḥrīr, we will include for prop. I.9, enclosed in double square brackets in bold face, the version found in Fez 1293 [1876], pp. 25-27. This text, however, seems to be identical to the so-called Pseudo-Ṭūsī notoriously disseminated in Europe by the Medicis in 1594 (sample comparisons seem to confirm this without doubt). The fact that the Fez 1293 edition is not the genuine Ṭūsī has not, as far as we are aware, been noted in the secondary literature.