1. Kellogg, O.D.: Foundations of Potential Theory 31 (1953)
2. Kilpeläinen, T., Malỳ, J.: Supersolutions to degenerate elliptic equations on quasi open sets. Comm. Partial Differ. Equ. 17(3–4), 371–405 (1992)
3. Malỳ, J., Ziemer, W.P.: Fine regularity of solutions of elliptic partial differential equations (51) (1997)
4. Kováčik, O., Rákosník, J.: On spaces $${L}^{p(x)}$$ and $${W}^{k, p(x)}$$. Czechoslov. Math. J. 41(4), 592–618 (1991)
5. Diening, L., Hästö, P., Nekvinda, A.: Open problems in variable exponent Lebesgue and Sobolev spaces. FSDONA04 proceedings, 38–58 (2004)