PLAZA, Ángel. Proof without words: four circles. Teaching Mathematics and Computer Science, [S. l.], v. 3, n. 2, p. 307–309, 2005. DOI: 10.5485/TMCS.2005.0097. Disponível em: https://ojs.lib.unideb.hu/tmcs/article/view/14754. Acesso em: 20 oct. 2024.