The Riesz theorem may refer to any of several mathematical theorems due to brothers Frigyes Riesz and Marcel Riesz: F. and M. Riesz theorem F. Riesz's theorem – Characterizes finite-dimensional Hausdorff topological vector spaces (TVSs). Riesz representation theorem M. Riesz extension theorem Riesz–Thorin theorem Riesz–Fischer theorem Riesz's lemma Riesz–Markov–Kakutani representation theorem