On the lifting and approximation theorem for nonsmooth vector fields
arXiv:1002.1331
Abstract
We prove a version of Rothschild-Stein's theorem of lifting and approximation and some related results in the context of nonsmooth Hormander's vector fields for which the highest order commutators are only Holder continuous. The theory explicitly covers the case of one vector field having weight two while the others have weight one.
46 pages, LaTeX. Minor changes in Section 3