2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/69483We discuss subsets $S$ of ${\mathbb{R}}^n$ such that every real valued function $f$ on $S$ is of the form {equation*} f(x_1,x_2,...,x_n) = u_1(x_1) + u_2(x_2) + ... + u_n(x_n), {equation*} and the related concepts and situations in analysis.10 pages, no figures, no tablesFunctional AnalysisGeneral Topologytext