$(INV)$ condition and regularity of the inverse
Anna Doležalová, Stanislav Hencl, Jani Onninen
TL;DR
The paper addresses the regularity of inverses for Sobolev mappings of finite distortion under the $(INV)$ condition. It constructs a generalized inverse $h$ that remains Sobolev with finite distortion and inherits the $(INV)$ property, even when the Jacobian may vanish on sets of positive measure, and extends the result to higher dimensions under $p>n-1$. A higher-dimensional analogue connects the $n$-harmonic energy of the inverse to the inner distortion of the forward map, enriching the variational perspective in Geometric Function Theory and nonlinear elasticity. The work articulates a robust framework for inverse maps in the $(INV)$ class, clarifying structural properties such as topological images, cavities, and a.e. differentiability, with implications for existence of (approximate) homeomorphic minimizers in elasticity models and Teichmüller-type energy problems in higher dimensions.
Abstract
Let $f \colon Ω\to Ω' $ be a Sobolev mapping of finite distortion between planar domains $Ω$ and $Ω'$, satisfying the $(INV)$ condition and coinciding with a homeomorphism near $\partialΩ$. We show that $f$ admits a generalized inverse mapping $h \colon Ω' \to Ω$, which is also a Sobolev mapping of finite distortion and satisfies the $(INV)$ condition. We also establish a higher-dimensional analogue of this result: if a mapping $f \colon Ω\to Ω' $ of finite distortion is in the Sobolev class $W^{1,p}(Ω, \mathbb{R}^n)$ with $p > n-1$ and satisfies the $(INV)$ condition, then $f$ has an inverse in $W^{1,1}(Ω', \mathbb{R}^n)$ that is also of finite distortion. Furthermore, we characterize Sobolev mappings satisfying $(INV)$ whose generalized inverses have finite $n$-harmonic energy.
