Eigenspaces of Families of Toeplitz Operators with Rational Matrix Symbols Kevin Clancey, Leiba Rodman (1983) Manuscripta mathematica
Erratum/addendum to the paper: "Quasi *-algebras and generalized inductive limits of C*-algebras" (Studia Math. 202 (2011), 165-190) Giorgia Bellomonte, Camillo Trapani (2013) Studia Mathematica
Error-estimates for the method of least squares of finding eigenvalues and eigenfunctions Karel Najzar (1970) Commentationes Mathematicae Universitatis Carolinae
Error-estimates for the Ritz's method of finding eigenvalues and eigenfunctions Karel Najzar (1971) Commentationes Mathematicae Universitatis Carolinae
Expansions in Generalized Eigenfunctions of Selfadjoint Operators. J. Weidmann, T. Poerschke, G. Stolz (1989) Mathematische Zeitschrift