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Dec 9, 2023 at 11:52 comment added Pietro Majer (for instance $X_k:=\{x: 1/k\le \|x\|\le 1-1/k\}$ is increasing and converges to $\overline B_1$ but $\partial X_k$ does not converge to $\partial B_1$)
Dec 7, 2023 at 17:31 comment added user111 Sure, I agree !
Dec 7, 2023 at 14:36 comment added Pietro Majer But the last implication is not immediate, although it's based on standard facts. Since it is the point of the question it seems safer to give a complete proof.
Dec 7, 2023 at 10:02 comment added user111 With the notations of the given answer, the sequence of sets $h(\overline B_r)$ gives an exhaustion of $U$ by compact sets, and it is known that the Hausdorff distance behaves well under increasing sequence of nonempty compact sets, namely $d_H(h(\overline B_r),\overline U)\to0$ as $r\to1$. In particular $d_H(\Gamma_r,\partial U)\to0$.
Dec 7, 2023 at 2:53 vote accept D.S. Lipham
Dec 6, 2023 at 23:22 answer added Pietro Majer timeline score: 2
Dec 6, 2023 at 17:10 history asked D.S. Lipham CC BY-SA 4.0