# integer

The set of integers, denoted by the symbol $\mathbb{Z}$, is the set $\{\dots-3,-2,-1,0,1,2,3,\dots\}$ consisting of the natural numbers  and their negatives.

Mathematically, $\mathbb{Z}$ is defined to be the set of equivalence classes   of pairs of natural numbers $\mathbb{N}\times\mathbb{N}$ under the equivalence relation $(a,b)\sim(c,d)$ if $a+d=b+c$.

• $(a,b)+(c,d):=(a+c,b+d)$

• $(a,b)\cdot(c,d):=(ac+bd,ad+bc)$

Typically, the class of $(a,b)$ is denoted by symbol $n$ if $b\leq a$ (resp. $-n$ if $a\leq b$), where $n$ is the unique natural number such that $a=b+n$ (resp. $a+n=b$). Under this notation, we recover the familiar representation of the integers as $\{\dots,-3,-2,-1,0,1,2,3,\dots\}$. Here are some examples:

• $0=$ equivalence class of $(0,0)=$ equivalence class of $(1,1)=\dots$

• $1=$ equivalence class of $(1,0)=$ equivalence class of $(2,1)=\dots$

• $-1=$ equivalence class of $(0,1)=$ equivalence class of $(1,2)=\dots$

The set of integers $\mathbb{Z}$ under the addition and multiplication operations  defined above form an integral domain  . The integers admit the following ordering relation making $\mathbb{Z}$ into an ordered ring: $(a,b)\leq(c,d)$ in $\mathbb{Z}$ if $a+d\leq b+c$ in $\mathbb{N}$.

Title integer Integer 2013-03-22 11:50:39 2013-03-22 11:50:39 CWoo (3771) CWoo (3771) 13 CWoo (3771) Definition msc 11-00 msc 03-00 rational integer $\mathbb{Z}$ Irrational