BUTTS, C. T. Social Network Analysis with sna. Journal of Statistical Software, [S. l.], v. 24, n. 6, p. 1–51, 2008. DOI: 10.18637/jss.v024.i06. Disponível em: https://www.jstatsoft.org/index.php/jss/article/view/v024i06. Acesso em: 15 aug. 2022.