Ostberg D., Perkins F. An introduction to linear analysis

Addison Wesley Publishing, 1966. — 792 p.As its title suggests, this book is an introduction to those branches of mathematics based on the notion of linearity. The subject matter in these fields is vast, ranging all the way from differential and integral equations and the theory of Hubert spaces to the mathematics encountered in constructing Green's functions and solving boundary-value problems in physics.
Needless to say, no single book can do justice to such a variety of topics, particularly when, as in the present case, it attempts to start at the beginning of things.
Nevertheless, it is the firm conviction of the authors that the notion of linearity which underlies these topics and ultimately enables them to be classified as branches of a single mathematical discipline can be developed in such a way that the student will gain a real understanding of the issues at stake.