The aim of this book is to give a systematic study of questions con-
cerning existence, uniqueness and regularity of solutions of linear
partial differential equations and boundary problems. Let us note
explicitly that this program does not contain such topics as
eigenfunction expan- sions, although we do give the main facts
concerning differential operators which are required for their study.
The restriction to linear equations also means that the trouble of
achieving minimal assumptions concerning the smoothness of the
coefficients of the differential equations studied would not be worth
while; we usually assume that they are infinitely differenti- able.
Functional analysis and distribution theory form the framework for the
theory developed here. However, only classical results of functional
analysis are used. The terminology employed is that of BOURBAKI. To make
the exposition self-contained we present in Chapter I the elements of
distribution theory that are required. With the possible exception of
section 1.8, this introductory chapter should be bypassed by a reader
who is already familiar with distribution theory.