“…Many problems in mathematical theory of generalized Newtonian fluids and mechanics of solids lead to the following question (compare, for example, the monographs of Málek, Necǎs, Rokyta and Růžička [36], Duvaut and Lions [11] as well as Zeidler [47]): Is it possible to control a certain energy depending on ∇v by the corresponding one depending just on Ev, that is, doesˆΩ |∇v| p dx c(p, Ω)ˆΩ |Ev| p dx (1.2) hold for functions v ∈W 1,p (Ω; R n )? As shown by Gobert [27]- [28], Necǎs [38], Mosolov and Mjasnikov [35], Temam [45], and later by Fuchs [19] the inequality (1.1) is true for all 1 < p < ∞. (It should be emphasized that inequality (1.1) does not hold in case p = 1; see [39], or [9].)…”