HANZEL, P. The finite subsets of natural numbers. Annales Universitatis Paedagogicae Cracoviensis Studia Mathematica, [S. l.], v. 3, p. 67–71, 2003. Disponível em: https://studmath.uken.krakow.pl/article/view/13469. Acesso em: 30 oct. 2026.