# The meaning of a notation from complex analysis

I have read the book Function Theory of Several Complex Variables of Krantz.But there is a notation I don't know what's it meaning. Can somebody give me a definition.Thank you. The notation is $\subset\subset$.For eample,let $\Omega\subset\subset R^{n}$ be a connected open set.Then what is the subset $\Omega$ . Thank you.

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As Zhen says, this notation usually means $\Omega$ is relatively compact in $R^n$. Why analysts tend to prefer this notation to saying "relatively compact in" or simply "bounded" if $R^n$ is involved will always remain a mystery to me... –  t.b. Aug 11 '11 at 11:00

There's an index of notation at the back of the book. Apparently, $\subset \subset$ means ‘relatively compact in’ and is defined in section 1.1.