Fishel, B. On two papers of Titchmarsh concerning eigenfunction expansions for partial differential operators of elliptic type. (English) Zbl 0049.35003 J. Lond. Math. Soc. 27, 496-502 (1952). PDFBibTeX XMLCite \textit{B. Fishel}, J. Lond. Math. Soc. 27, 496--502 (1952; Zbl 0049.35003) Full Text: DOI
Fishel, B. The continuous spectra of certain differential equations. (English) Zbl 0048.06703 J. Lond. Math. Soc. 27, 175-180 (1952). PDFBibTeX XMLCite \textit{B. Fishel}, J. Lond. Math. Soc. 27, 175--180 (1952; Zbl 0048.06703) Full Text: DOI