This book could be used either for self-study or as a course text, and aims to lead the reader to the more advanced literature on partial differential operators.

A revolutionary book that for the first time provided a rigorous mathematical framework for quantum mechanics. -- Google books

This book is an updated version of the classic 1987 monograph "Spectral Theory and Differential Operators".The original book was a cutting edge account of the theory of bounded and closed linear operators in Banach and Hilbert spaces ...

This book was written to remove this isolation.

General spectral theory; Riesz operators; Hermitian operators; Prespectral operators; Well-bounded operators.

The interconnections among the various topics are clarified both by the use of vector spaces as a central unifying theme, recurring throughout the book, and by putting ideas into their historical context.