The basic approximation theorem you might be thinking of is known as Kolmagorov's Theorem (dude got around). It's an early theorem, from 1957, that's about the

The basic approximation theorem you might be thinking of is known as Kolmagorov's Theorem (dude got around). It's an early theorem, from 1957, that's about the universality of functions of a linear combination of single variable function. But all the other universality theorems refer back to it and don't have their own names, for example; Optimal approximation of continuous functions by very deep ReLU networks by Dmitry Yarotsky [1]. The reference for the original theorem would be On The Structure Of Continuous Functions Of Several Variable, David A. Sprecker [2], [1] http://proceedings.mlr.press/v75/yarotsky18a http://proceedings.mlr.press/v75/yarotsky18a [2] https://www.ams.org/journals/tran/1965-115-00/S0002-9947-1965-0210852-X/S0002-9947-1965-0210852-X.pdf https://www.ams.org/journals/tran/1965-115-00/S0002-9947-196...