Balls and metrics defined by vector fields. I: Basic properties
The authors study the basic properties of certain balls and metrics that are naturally induced from a given family of vector fields. These properties are used to obtain estimates for the kernels of approximate inverses of some non-elliptic partial differential operators, such as Hörmander's sum of squares. Some of the present properties were announced earlier by the authors in Proc. Natl. Acad. Sci. USA 78, 6596-6599 (1981; Zbl 0517.32002). In that paper, they also announced applications of these balls and metrics to problems concerning the boundary behavior of holomorphic functions in domains of finite type. The details of these applications will, according to the authors, appear in another paper.
boundary behavior of holomorphic functions
scientific article; zbMATH DE number 3925275