1. [3] M. Heins, On the Lindelf principle, Ann. Math., 61 (1955), 440-473.
2. [4] D. A. Herron and P. Koskela, Continuity of Sobolev functions and Dirichlet finite harmonic measures, Potential Analysis (to appear).
3. [1] E. Gagliardo, Caractterizzazione delle traccie sulla frontiera relative ad alcune classi di funzioni in n variabili, Rend. Sem. Mat. Padova, 27 (1957), 284-305.
4. [2] J. Heinonen, T. Kilpelainen and O. Martio, Nonlinear Potential Theory of Degenerate Elliptic Equations, Claredon Press, Oxford-New York-Tokyo, 1993.
5. [5] L. Holopainen, Nonlinear potential theory and quasiregular mappings on Riemannian manifolds, Ann. Acad. Sci. Fenn., Ser. AI Math. Dissertation, 74 (1990), 1-45.