Walsh, J. L. A closed set of normal orthogonal functions. (English) JFM 49.0293.03 Am. J. Math. 45, 5-24 (1923). Reviewer: Hellinger, Prof. (Frankfurt a. M.) MSC: 42C05 PDFBibTeX XMLCite \textit{J. L. Walsh}, Am. J. Math. 45, 5--24 (1923; JFM 49.0293.03) Full Text: DOI Link
Menchoff, D. Sur les séries de fonctions orthogonales. I: La convergence. (French) JFM 49.0293.01 Fundam. Math. 4, 82-105 (1923). Reviewer: Rosenthal, Prof. (Heidelberg) MSC: 40A30 33C45 42C05 PDFBibTeX XMLCite \textit{D. Menchoff}, Fundam. Math. 4, 82--105 (1923; JFM 49.0293.01) Full Text: DOI EuDML