L. Capogna et al., CAPACITARY ESTIMATES AND THE LOCAL BEHAVIOR OF SOLUTIONS OF NONLINEARSUBELLIPTIC EQUATIONS, American journal of mathematics, 118(6), 1996, pp. 1153-1196
We establish sharp capacitary estimates for Carnot-Caratheodory rings
associated to a system of vector fields of Hormander type. Such estima
tes are instrumental to the study of the local behavior of singular so
lutions of a wide class of nonlinear subelliptic equations. One of the
main results is a generalization of fundamental estimates obtained in
dependently by Sanchez-Calle and Nagel, Stein and Wainger.