Mafra, A. C., and M. Tavares. “A Criterion for Bijectivity of Mappings of Euclidean Spaces”. Topological Methods in Nonlinear Analysis, vol. 43, no. 1, Apr. 2016, pp. 117-28, https://apcz.umk.pl/TMNA/article/view/TMNA.2014.008.