L’insieme quoziente delle congruenze $\Z/_\equiv$ è definito come
$$ \Z/\equiv = \{[a]\equiv : a \in \Z \} = \left\{ \underbrace{[0]}{r=0}, \underbrace{[1]}{r=1}, \underbrace{[2]}{r=2}, \dots, \underbrace{[m-1]}{r=m-1} \right\} $$