%0 Journal Article
%A Shing-Tung Yau
%A Huai-Dong Cao
%T Gradient estimates, Harnack inequalities and estimates for heat kernels of the sum of squares of vector fields.
%J Mathematische Zeitschrift
%D 1992
%P 485-504
%V 211
%N 3
%I mathdoc
%U http://geodesic.mathdoc.fr/item/MZ_1992__211_3_174454/
%F MZ_1992__211_3_174454