Hedberg, Lars Inge: Nonlinear potential theory and Sobolev spaces.
(English).
In:
Krbec, Miroslav, Kufner, Alois
and Rákosník, Jiří (eds.): Nonlinear Analysis, Function Spaces and Applications, Proceedings of the Spring School held in Litomyšl, 1986.
Vol. 3.
BSB B. G. Teubner Verlagsgesellschaft, Leipzig, 1986.
pp. 5-30