Koskela, Pekka: Metric Sobolev spaces.
(English).
In:
Opic, Bohumír
and Rákosník, Jiří (eds.): Nonlinear Analysis, Function Spaces and Applications, Proceedings of the Spring School held in Prague, July 17-22, 2002.
Vol. 7.
Czech Academy of Sciences, Mathematical Institute, Praha, 2003.
pp. 133-147