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Numerical ranges of operators on normed spaces and of elements of normed algebras. (English) Zbl 0207.44802
London Mathematical Society Lecture Note Series. 2. London: Cambridge University Press. ii, 142 p. (1971).

47-02 Research exposition (monographs, survey articles) pertaining to operator theory
47A12 Numerical range, numerical radius
47A10 Spectrum, resolvent
47B15 Hermitian and normal operators (spectral measures, functional calculus, etc.)
47C05 Linear operators in algebras