%0 Journal Article
%A Antonio Sánchez-Calle
%T Fundamental solutions and geometry of the sum of squares of vector fields.
%J Inventiones mathematicae
%D 1984
%P 143-160
%V 78
%I mathdoc
%U http://geodesic.mathdoc.fr/item/IM_1984__78_143171/
%F IM_1984__78_143171