ABSTRACT
This is a service chapter, in the sense that it can be skipped in a first reading. We begin by listing various function spaces which play a fundamental role in the modern approach to partial elliptic and parabolic differential equations (Section 1.1.1). We then recall (without proofs) some basic results on interpolation, density, extensions, and traces, as well as local representations of boundary portions and some elementary relations which are used later on several times.
