Looking for an original citation of Cantor It seems that Cantor rather than Cauchy suggested the Cauchy equivalence class definition of $\mathbb{R}$. I am looking for the original book or paper (for whomever originally suggested the Cauchy definition.) My question is: what is the citation for this original source?

See Cantor's definition of real number:

> Georg Cantor, Ueber die Ausdehnung eines Satzes aus der Theorie der trigonometrischen Reihen (1872).