Introduction: Notation, Elementary Results

Abstract

We start this chapter by listing some basic concepts, which are or should be wellknown — but it is good sometimes to return to basics. This gives us the opportunity of making precise the system of notation used in this book. For example, some readers may have forgotten that “i.e.” means id est, the literal translation of “that is (to say)”. If we get closer to mathematics, S∖{x} denotes the set obtained by depriving a set S function of a point x ∈ S. We also mention that, if f is a function, f ⁻¹ (y) is the inverse image of y, i.e. the set of all points x such that f(x) = y. When f is invertible, this set is the singleton {f ⁻¹(y)}.