Wolff-potential estimates and doubling of subelliptic pp-harmonic measures

Let X={X1,…,Xm} be a system of C∞C∞ vector fields in RnRn satisfying Hörmander’s finite rank condition and let ΩΩ be a non-tangentially accessible domain with respect to the Carnot–Carathéodory distance dd induced by XX. We prove the doubling property of certain boundary measures associated to non-negative solutions, which vanish on a portion of ∂Ω∂Ω, to the equation LA,pu=∑i=1mXi∗Ai(x,Xu)=0. Given pp, 1