Fedorchuk, V. M., & Fedorchuk, V. I. (2004). 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, 4, 65–74. Retrieved from https://studmath.uken.krakow.pl/article/view/13309