Ursescu theorem
In mathematics, particularly in functional analysis and convex analysis, the Ursescu theorem is a theorem that generalizes the closed graph theorem, the open mapping theorem, and the uniform boundedness principle. == Ursescu theorem == The following notation and notions are used, where R : X ⇉ Y {\displaystyle {\mathcal {R}}:X\rightrightarrows Y} is a set-valued function and S {\displaystyle S} is a non-empty subset of a topological vector space X {\displaystyle X} : the affine span of S {\displaystyle S} is denoted by aff S {\displaystyle \operatorname {aff} S} and the linear span is denoted by span S .