Named in honor of Leopold Vietoris (b. 1891), professor emeritus of mathematics of the Leopold-Franzens-University in Innsbruck, on the occasion of his forthcoming 107th birthday. Vietoris is the oldest full member of the Austrian Academy of Sciences and a highly decorated scientist. He made fundamental contributions to algebraic and set-theory topology, and he also wrote outstanding papers on the theory of real functions and on applied mathematics. Named by the first discoverer following a suggestion by H. Haupt, who prepared the citation.