<p style='text-align: justify;'>Bifolium from a Judaeo-Arabic version of ʿAlī ibn ʿĪsā, Taḏkirat al-kaḥḥālīn (‘Memorandum for opticians’), first discourse, chapter 14, heading of chapter 15, chapter 17 and beginning of chapter 18 (ed. Hyderabad 1964, pp. 26-27, 29-31).</p>