%0 Journal Article
%A D. Müller
%A F. Ricci
%T Analysis of second order differential operators on Heisenberg groups. I.
%J Inventiones mathematicae
%D 1990
%P 545-582
%V 101
%N 2
%I mathdoc
%U http://geodesic.mathdoc.fr/item/IM_1990__101_2_143816/
%F IM_1990__101_2_143816