Nussbaum, R. D. The radius of the essential spectrum. (English) Zbl 0216.41602 Duke Math. J. 37, 473-478 (1970). Cited in 138 Documents MSC: 47A10 Spectrum, resolvent PDFBibTeX XMLCite \textit{R. D. Nussbaum}, Duke Math. J. 37, 473--478 (1970; Zbl 0216.41602) Full Text: DOI