FENILLE, M. C. The trivial homotopy class of maps from two-complexes into the real projective plane. Topological Methods in Nonlinear Analysis, [S. l.], v. 46, n. 2, p. 603–616, 2015. DOI: 10.12775/TMNA.2015.060. Disponível em: https://apcz.umk.pl/TMNA/article/view/TMNA.2015.060. Acesso em: 18 jan. 2022.