Mittag-Leffler, Magnus Gösta (mängˈnŏs yöˈstä mĭtˈäg-lĕfˈlər) [key], 1846–1927, Swedish mathematician. He was (1877–81) professor at Helsingfors (Helsinki) and at the Univ. of Stockholm from 1881. In 1882 he founded Acta Mathematica, which he edited until his death. He made important contributions to analysis (including the Mittag-Leffler theorem on single-valued functions) and to linear differential equations and greatly stimulated mathematical research.