next up previous contents
Next: The natural numbers Up: Discrete Mathematics Previous: Conjugacy classes in   Contents

The classical sets of numbers

The following notations are standard notations.

Notation 3   The ``natural numbers'', whose set is denotet by $ \mathbb{N}$, are

$\displaystyle \{ 0, 1,2,3,\dots \}.$    

The integers are

$\displaystyle \{ \dots, -2, -1, 0, 1, 2, 3, \dots \}.$    

The set of all the integers is denoted by $ \mathbb{Z}$; the set of all the non-negative integers is equal to $ \mathbb{N}$ and is sometimes denoted also by $ \mathbb{Z}^+$ and the set of non positive integers is denoted by $ \mathbb{Z}^-$. There are also the rational numbers, whose set is denoted by $ \mathbb{Q}$ and the set of real numbers, denoted by $ \mathbb{R}$.

Actually, these sets are generally assumed to be ``well known'', but most students never saw their construction. We will devote the following sections to these constructions.


root 2002-06-10