MEYER, D.; HORNIK, K. Generalized and Customizable Sets in R. Journal of Statistical Software, [S. l.], v. 31, n. 2, p. 1–27, 2009. DOI: 10.18637/jss.v031.i02. Disponível em: https://www.jstatsoft.org/index.php/jss/article/view/v031i02. Acesso em: 23 may. 2022.