{0,S(0),S(S(0)),S(S(S(0))),S(S(S(S(0)))),S(S(S(S(S(0))))),S(S(S(S(S(S(0)))))),S(S(S(S(S(S(S(0))))))),...} |__| |_____| |________| |___________| |______________| |_________________| |____________________|que l'on note le plus souvent :
{0,1,2,3,4,5,6,7,...}