On the convergence of Laplace-Beltrami operators associated to quasiregular mappings Ricardo de Arcangelis; Patrizia Donato — 1987 Studia Mathematica
A characterization of sets of functions and distributions on ℝ n described by constraints on the gradient. Corbo Esposito, Antonio; De Arcangelis, Ricardo — 1996 Journal of Convex Analysis