FREILING, G.; RYKHLOV, V. Pointwise convergence of eigenfunction expansions for a general class of regular eigenvalue problem. Methods of Functional Analysis and Topology, [S. l.], v. 3, n. 2, p. 27–45, 1997. Disponível em: https://zen.imath.kiev.ua/index.php/mfat/article/view/35. Acesso em: 19 dec. 2025.