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Let $\{X_i^n\}$ be a sequence of $n$-dimensional Alexandrov spaces with curvature uniformly bounded from below which converges in the Gromov-Hausdorff sense to a compact $n$-dimensional Alexandrov space (i.e. without collapse). Let $E_i\subset X_i$ be extremal subsets. Assume that $E_i$ converge to a compact subset $E\subset X$ in the Hausdorff sense.

Is it true that $E$ is an extremal subset of $X$?

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1 Answer 1

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The limit of extremal subsets is an extremal subset, see Lemma 4.1.3 in Petrunin's Semiconcave functions in Alexandrov geometry. The non-collapsing assumption is not needed.

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