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A generalized Stoilow decomposition for pairs of mappings of integrable dilatation

We prove a rigidity result for pairs of mappings of integrable dilatation whose gradients pointwise deform the unit ball to similar ellipses. Our result implies as corollaries a version of the generalized Stoilow decomposition provided by Theorem 5.5.1 of a recent monograph of Astala-Iwaniec-Martin and the two dimensional rigidity result of our previous paper for mappings whose symmetric part of gradient agrees. Specifically let $u,v\in W^{1,2}(Ω,\mathbb{R}^2)$ where $\det(Du)>0$, $\det(Dv)>0$ a.e. and $u$ is a mapping of integrable dilatation. Suppose for a.e. $z\in Ω$ we have $Du(z)^T Du(z)=λDv(z)^T Dv(z)$ for some $λ>0$. Then there exists a meromorphic function $ψ$ and a homeomorphism $w\in W^{1,1}(Ω:\mathbb{R}^2)$ such that $Du(z)=\mathcal{P}(ψ(w(z)))Dv(z)$ where $\mathcal{P}(a+ib)=(\begin{smallmatrix} a & -b \\ b & a \end{smallmatrix})$. We show by example that this result is sharp in the sense that there can be no continuous relation between the gradients of $Du$ and $Dv$ on a dense open connected subset of $Ω$ unless one of the mappings is of integrable dilatation.