Wiener's Tauberian theorem
In mathematical analysis, Wiener's Tauberian theorem is any of several related results proved by Norbert Wiener in 1932. They provide a necessary and sufficient condition under which any function in L 1 {\displaystyle L^{1}} or L 2 {\displaystyle L^{2}} can be approximated by linear combinations of translations of a given function.
Source: Wikipedia — Wiener's Tauberian theorem (CC BY-SA 4.0)