Abstract:
Necessary and sufficient conditions for extending a sequence of functions to a complete orthonormal system on a larger set are indicated. As an application of the extension problem, a description of the space of coefficients of orthogonal series in a complete bounded system, converging on sets of positive measure, is given.
Citation:
A. M. Olevskii, “On the extension of a sequence of functions to a complete orthonormal system”, Mat. Zametki, 6:6 (1969), 737–747; Math. Notes, 6:6 (1969), 908–913