2 citations to https://www.mathnet.ru/rus/tm615
  1. Il'in V.A., “on a Generalization of Bessel'S Inequality and the Riesz-Fischer Theorem To the Case of Expansions of Functions in l (P) With P Not Equal 2 in Eigenfunctions of the Laplace Operator on An Arbitrary N-Dimensional Domain”, Dokl. Math., 90:1 (2014), 407–411  crossref  mathscinet  zmath  isi  scopus  scopus
  2. Gavrilov V.V., “An analog of the Riesz–Fischer theorem for the Fourier transform corresponding to a one–dimensional Schrodinger operator with measurable bounded potential”, Differential Equations, 33:8 (1997), 1022–1027  mathnet  mathscinet  zmath  isi