%0 Journal Article %A V. A. Il'in %T Riesz means, Ces\`aro and Poisson--Abel summability of Fourier series of eigenfunctions %J Differencialʹnye uravneniâ %D 1966 %P 816-827 %V 2 %N 6 %I mathdoc %U http://geodesic.mathdoc.fr/item/DE_1966_2_6_a9/ %G ru %F DE_1966_2_6_a9