Jy. Chemin et Cj. Xu, SOBOLEV IMBEDDINGS, WEYL-HORMANDER CALCUL US AND SUBELLIPTIC VECTOR-FIELDS, Annales Scientifiques de l'Ecole Normale Superieure, 30(6), 1997, pp. 719-751
Ln this paper, we study Sobolev embedding theorem for a class of weigh
ted Sobolev space defined by a system of vector fields satisfying the
Hormander condition.