General Formalism

Abstract

In this chapter we develop the general background information relevant to the subsequent analysis. Part of the material consists of standard results which are summarized for later reference. A second part consists of the basic definitions of subelliptic operators and the related semigroups together with the description of some preliminary results which motivate the later analysis. Thirdly, we introduce several techniques adapted to the Lie group analysis. Since most of the reference material is quite standard it is summarized in formal statements without proof. Further details and specific references to the literature are, however, given in the Notes and Remarks at the end of the chapter.