Some Definitions and Theorems

Abstract

The present chapter collects some of the main definitions and theorems on which the problems in the previous chapters rely, with special attention to those elements of the theory that sometimes give rise to confusion due to a lack of general agreement in the literature on the precise formulation and/or notation.

We have included the definitions and theorem in a section for each previous chapter of the book. As explained in the Preface, proofs are not included, mainly because the book is not intended as a handbook on the topics studied, but only as a practical complement to the courses, often found on excellent books, like those cited in the References. On the other hand, we have tried to use a more or less standard notation and terminology.