1. Numerical Ranges of Operators on Normed Spaces and of Elements of Normed Algebras;Bonsall,1971
2. Numerical Ranges, II;Bonsall,1973
3. Convolution Operators and Factorization of Almost Periodic Matrix Functions;Böttcher,2002
4. A Course in Functional Analysis;Conway,1990
5. Linear Operators, Part I;Dunford,1988