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• D.L. Black, “Avicenna on the Ontological and Epistemic Status of Fictional Beings.” Documenti e studi sulla tradizione filosofica medievale 8 (1997), 425-53.

• D.L. Black, “Mental Existence in Thomas Aquinas and Avicenna.” Mediaeval Studies 61 (1999), 45–79.

• T.-A. Druart, “Shay’ or Res as Concomitant of ‘Being’ in Avicenna,” Documenti e Studi sulla Tradizione Filsofica Medievale 12 (2001), 125-42.

• A.M. Goichon, La distinction de l’essence et l’existence d’après ibn Sina (Avicenne) (Paris: 1937).

• O. Lizzini, “Wujūd-Mawjūd/Existence-Existent in Avicenna: a Key Ontological Notion of Arabic Philosophy,” Quaestio 3 (2003), 11-38.

• F. Rahman, “Essence and Existence in Avicenna,” Mediaeval and Renaissance Studies 4 (1958), 1-16.

• R. Wisnovsky, “Notes on Avicenna’s Concept of Thingness (shay’iyya),” Arabic Sciences and Philosophy 10 (2000), 181-221.