found: Ibn Ḥazm, A. i. A. De ring ... c1977 (a.e.)title page (J. J. Witkam)
found: Mystical illustrations from the teachings of Syaikh Ahmad al-Qusyasyi, 1995:title page (Jan Just Witkam)
found: Brockelmann, Carl. History of the Arabic written tradition, 2016:title page (with a preface by Jan Just Witkam)
found: National Library of the Netherlands online catalogue, 25 January 2001(access point: Witkam, Januarius Justus, 1945-)
found: Jan Just Witkam's personal website, viewed March 30, 2017(Professor Jan Just Witkam; Dr. Jan Just Witkam, emeritus-professor of Codicology and Paleography of the Islamic World, in the University of Leiden, Leiden, The Netherlands; born 1945 in Leiden)
