1. Heinz Bachmann: Transfinite Zahlen. Springer, Berlin (1967)
2. Felix Bernstein: Untersuchungen aus der Mengelehre. Dissertation, University of Göttingen (Germany) (1901)
3. Felix Bernstein: Untersuchungen aus der Mengelehre. Math. Ann. 61, 117–155 (1905)
4. Georg Cantor: Beiträge zur Begründung der transfiniten Mengenlehre. I./II. Math. Ann. 46/49, 481–512 (1895/1897), 207–246 (see [5] for a translation into English)
5. Georg Cantor: 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 (1915) [reprint: Dover, New York (1952)]