What does $K \Subset U$ mean? I think that $K$ is a compact set with, $K \subset \subset U$ (precompact), where $U$ is an open set. Am I right? Thank you.
What does $K \Subset U$ mean?
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notation
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2I've always been under the impression that in analysis or PDE contexts, the difference between $\Subset$ and $\subset\subset$ is the difference of using $\langle,\rangle$ versus <,>, namely one of typography. (Or, perhaps a better example is using << versus $\ll$.) – 2012-10-09
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I have seen $K\subset\subset G$ if $K$ is compact, $G$ is open and $K\subseteq G$. I have seen it used in the context of locally compact topological spaces.