Spectra of products and numerical ranges

Semi-inner-product spaces

G. Lumer · Transactions of the American Mathematical Society · 1961 · 474 citations · Full text

Hilbert Space Considerations, Linear Operator, Representation Theory +5

A proof that every Banach space is subreflexive

Errett Bishop, R. R. Phelps · Bulletin of the American Mathematical Society · 1961 · 325 citations · Full text

Interpolation Space, Preprint, Real World Evidence +15

The closure of the numerical range contains the spectrum

Eduardo H. Zarantonello · Bulletin of the American Mathematical Society · 1964 · 75 citations · Full text

Spectral Theory, Riemann-hilbert Problem, Numerical Range +2

The numerical range of a normal operator

S. K. Berberian · Duke Mathematical Journal · 1964 · 34 citations

Linear Operator, Engineering, Riemann-hilbert Problem +4