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Jan 14, 2021 at 9:54 vote accept Asaf Shachar
Oct 26, 2020 at 18:59 history edited mlk CC BY-SA 4.0
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Oct 26, 2020 at 18:51 comment added mlk @AsafShachar Ah, yeah I forgot that detail. However the fix is easy. Since $\Omega_1$ has $C^1$ boundary there is an extension operator for $W^{1,2}$. So we can extend $f_n$ to $\Omega \supset \Omega_1$ with the same convergence and then $\overline{\Omega_1}$ is compact within $\Omega$.
Oct 26, 2020 at 17:42 comment added Asaf Shachar I don't think that it's trivial to guarantee this, since even though $f \in C^1$, we don't know that it's injective (yet), so $A$ may well have some weird pre-images which are close to the boundary of $\Omega_1$
Oct 26, 2020 at 17:40 comment added Asaf Shachar Thanks, that looks like a nice solution! I have one question: Müller's result gives weak convergene of the Jacobians on $L^1(K)$ for compactly contained subsets $K \subset \subset \Omega_1$. So, for your argument to work you need to make sure that $B=f^{-1}(A)$ is compactly contained in the interior $\Omega_1$. (I actually think that you need it also for the first $\liminf$ inequality $\int_B \det df dx \leq \liminf_{n\to\infty} \int_B \det df_n dx $.)
Oct 26, 2020 at 16:38 history edited mlk CC BY-SA 4.0
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Oct 26, 2020 at 16:31 history answered mlk CC BY-SA 4.0