I kitea e Weierstrass, Cantor, me Heine a rātou ariā i runga i ngā rangatū mutunga kore mutunga kore, i te kitenga o Dedekind i a runga i te ariā o tētahi tapahanga (Schnitt) i roto i te pūnaha o ngā tau haumarutanga katoa, e wehe ana i a rātou ki ngā rōpū e rua whai āhuatanga.