1. D. Aalto and J. Kinnunen, Maximal functions in Sobolev spaces, in Sobolev Spaces in Mathematics I, Springer, Berlin, 2008, pp. 25–68.
2. J. M. Aldaz and J. Pérez Lázaro, Boundedness and unboundedness results for some maximal operators on functions of bounded variation, J. Math. Anal. Appl. 337 (2008), 130–143.
3. C. Bennett, R. A. DeVore and R. Sharpley, Weak L ∞ and BMO, Ann. of Math. (2) 113 (1981), 601–611.
4. C. Bennett and R. Sharpley, Interpolation of Operators, Academic Press, New York, 1988.
5. A. Björn and J. Björn, Nonlinear potential theory on metric spaces, in preparation.