Abstract
This article addresses the conceptual questions of quasiconformal analysis on Carnot groups. We prove the equivalence of the three classes of homeomorphisms: the mappings of the first class induce bounded composition operators from a weighted Sobolev space into an unweighted one; the mappings of the second class are characterized by way of estimating the capacity of the preimage of a condenser in terms of the weighted capacity of the condenser in the image; the mappings of the third class are described via a pointwise relation between the norm of the matrix of the differential, the Jacobian, and the weight function. We obtain a new proof of the absolute continuity of mappings.
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Notes
A horizontal curve is a piecewise smooth path whose tangent vector at each point where it exists lies in \( V_{1} \).
If \( dx \) is the volume form on \( 𝔾 \) of degree \( N \), then \( i(X_{1j})\,dx \) is a form of degree \( N-1 \), which takes the values \( (i(X_{1j})\,dx)(Y_{1},Y_{2},\dots,Y_{N-1})=dx(X_{1j},Y_{1},Y_{2},\dots,Y_{N-1}) \) on the smooth vector fields \( Y_{1},Y_{2},\dots,Y_{N-1} \) defined on \( 𝔾 \).
Here \( B_{\delta} \) is an arbitrary ball \( B(x,\delta)\subset D^{\prime} \) containing the point \( y \).
The measure of the image \( \varphi(A) \) vanishes for every set \( A\subset D\setminus Z \) of measure zero.
By the regularity of Lebesgue measure, we can express every measurable set \( A\in D\setminus\Sigma \) as the disjoint union of a Borel set and a set of measure zero; the image of the Borel set under the homeomorphism \( \varphi \) is a Borel set, while by Luzin’s \( \mathcal{N} \)-property the image of each set of measure zero is a set of measure zero.
The definition of generalized derivatives assumes that \( \frac{\partial u}{\partial y_{j}}\in L_{1,\operatorname{loc}}(D^{\prime}) \).
Henceforth \( \operatorname{Lip}_{l}(D^{\prime}) \) stands for the space of locally Lipschitz functions on \( D^{\prime} \). It is obvious that \( \operatorname{Lip}_{l}(D^{\prime})=W^{1}_{\infty,\operatorname{loc}}(D^{\prime})\cap C(D^{\prime}) \).
Here (3.2) should be interpreted as follows: The function \( u\in{L}^{1}_{p}(U;\omega)\cap\overset{\circ}{\operatorname{Lip}}_{l}(U) \), extended by zero beyond \( U \), lies in \( {L}^{1}_{p}(D^{\prime};\omega)\cap\operatorname{Lip}_{l}(D^{\prime}) \).
Note that here the conditions \( u_{i}\in\mathcal{R}(U_{i}) \) and \( v_{i}=\varphi^{*}u_{i} \) are redundant.
Here, in order to preserve the notational logic, we should write \( \mathcal{A}(E)\cap{L}^{1}_{p}(D^{\prime};\omega)\cap\operatorname{Lip}_{l}(D^{\prime}) \) for the class of admissible functions for a condenser. However, we avoid that because there is always \( u\in\mathcal{A}(E)\cap\operatorname{Lip}_{l}(D^{\prime}) \) for which the norm (3.1) is finite, and this guarantees that the capacity is finite.
Henceforth \( B^{E}(a,r) \) stands for the Euclidean ball of radius \( r \) and center \( a \).
Note that the right-hand side of (3.18) holds for the arbitrary constant \( K_{p} \) and quasiadditive set function \( \Psi \) in (3.17), while the left-hand side of (3.18) follows from the right-hand side on assuming that \( K_{p} \) and the quasiadditive set function \( \Psi \) are optimized using (3.21) and (3.22).
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The work was carried out in the framework of the State Task to the Sobolev Institute of Mathematics (Project 0314–2019–0006).
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Translated from Sibirskii Matematicheskii Zhurnal, 2022, Vol. 63, No. 2, pp. 283–315. https://doi.org/10.33048/smzh.2022.63.204
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Vodopyanov, S.K., Evseev, N.A. Functional and Analytical Properties of a Class of Mappings of Quasiconformal Analysis on Carnot Groups. Sib Math J 63, 233–261 (2022). https://doi.org/10.1134/S0037446622020045
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DOI: https://doi.org/10.1134/S0037446622020045