TY  - JOUR
AU  - Antonio Sánchez-Calle
TI  - Fundamental solutions and geometry of the sum of squares of vector fields.
JO  - Inventiones mathematicae
PY  - 1984
SP  - 143
EP  - 160
VL  - 78
PB  - mathdoc
UR  - http://geodesic.mathdoc.fr/item/IM_1984__78_143171/
ID  - IM_1984__78_143171
ER  -