FEDORCHUK, V. M.; FEDORCHUK, V. I. On the differential first-order invariants for the non-splitting subgroups of the generalized Poincaré group P(1,4). Annales Universitatis Paedagogicae Cracoviensis Studia Mathematica, [S. l.], v. 4, p. 65–74, 2004. Disponível em: https://studmath.uken.krakow.pl/article/view/13309. Acesso em: 30 oct. 2026.