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$\newcommand{\intr}{\mathrm{int}}$

I need to give an example of a metric space $(X,d)$ and $A ⊆ X$ so that $\overline{\intr(A)} ⊂ \intr (\overline{A})$, where $\overline{B}$ refers to the closure of $B$.

Also, another $X,A$ where there is no containment relation beween the two.

I've found simple examples for $\overline{\intr(A)} ⊃ \intr(\overline{A})$ and for equality, but I'm guessing I need to look further afield here.

I'd appreicate any hints.

GregRos
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1 Answers1

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With the usual metric on $\mathbb{R}$, Let $ X=\mathbb{R}$ and $A= \mathbb{Q}$.

  • Doh. Damn my intuition. I thought the interior of $ℚ$ in $ℝ$ would just be $ℚ$, but that's actually obviously wrong. Thnak you. – GregRos Apr 01 '14 at 12:25