Source: http://web.a9lame.com/Documents/Lyc%C3%A9e/Bac%20FR/a-Tronc%20commun%20International/a-Tronc%20commun%20Science/a-Math%C3%A9matiques/a-Semestre%20I/b-Les%20ensembles%20de%20nombres%20N,%20Z,%20Q,%20D%20et%20R/a-Cours/Cours%202%20Les%20ensembles%20de%20nombres%20N,%20Z,%20Q,%20D%20et%20R.pdf