have received much attention recently. See, for example, [5, 7, 9, 18, 26, 27, 28]. Problem (1.1) arises in the theory of quasiregular and quasiconformal mappings or in the study of non-Newtonian fluids. In the latter case, the pair (p,q) is a characteristic of the medium. Media with (p,q) > (2,2) are called dilatant fluids and those with (p,q) < (2,2) are… (More)