Published online by Cambridge University Press: 30 May 2022
For a domain G in the one-point compactification $\overline{\mathbb{R}}^n = {\mathbb{R}}^n \cup \{ \infty\}$ of ${\mathbb{R}}^n, n \geqslant 2$ , we characterise the completeness of the modulus metric $\mu_G$ in terms of a potential-theoretic thickness condition of $\partial G\,,$ Martio’s M-condition [ 35 ]. Next, we prove that $\partial G$ is uniformly perfect if and only if $\mu_G$ admits a minorant in terms of a Möbius invariant metric. Several applications to quasiconformal maps are given.
The authors were supported in part by JSPS KAKENHI Grant Number JP17H02847 and NSF of the Higher Education Institutions of Jiangsu Province, China, Grant Number 17KJB110015, and NSFC Grant Number 12001391.