1. Heinz Bachmann, Transfinite Zahlen, Springer-Verlag, Berlin ⋅ Heidelberg, 1967.
2. Felix Bernstein, Untersuchungen aus der Mengelehre, Dissertation (1901), University of Göttingen (Germany).
3. ——, Untersuchungen aus der Mengelehre, Mathematische Annalen, vol. 61 (1905), 117–155.
4. Georg Cantor, Beiträge zur Begründung der transfiniten Mengenlehre. I./II., Mathematische Annalen, vol. 46/49 (1895/1897), 481–512/207–246 (see [5] for a translation into English).
5. ——, Contributions to the Founding of the Theory of Transfinite Numbers, (translation into English of [4]), [translated, and provided with an introduction and notes, by Philip E. B. Jourdain], Open Court Publishing Company, Chicago and London, 1915 [reprint: Dover Publications, New York, 1952].