ABSTRACT
The purpose of this chapter is twofold: (1) to introduce and discuss in some detail a number of mathematical aspects that will be used in the following chapters, and (2) to provide the reader with some concepts, notions and results that are prerequisites for a more advanced and more mathematically oriented approach to the subject matter of this text. In this light, some sections of this chapter can be skipped in a rst reading and considered only after having read the subsequent chapters, in particular Chapters 5-9.
