We all take for granted the theorem that every ordinal $\alpha > 0$ has a Cantor normal form, and there are plenty of proofs of it, some of which are on this site. However, where was it proved? Was it actually proved by Cantor in his 1883 paper introducing ordinals? Or somewhere else?



Where was the Cantor normal form theorem first proved?
Cantor proved the normal form theorem in his 1895 paper [Beiträge zur Begründung der transfiniten Mengenlehre](https://eudml.org/doc/157768), which was his last paper on transfinite set theory.


