<p style='text-align: justify;'>Bifolium from a Judaeo-Arabic version of ʿAlī ibn ʿĪsā, Taḏkirat al-Kaḥḥālīn (‘Memorandum for opticians’), from the first discourse, chapters 15-17 and beginning of the second discourse (ed. Hyderabad 1964, pp. 27-30, 51-55).</p>