Chapter 11: Problem 4
Prove that \((0,1]=\bigcap_{n=1}^{\infty}(0,1+1 / n)\), as asserted in Example \(11.1 .6(\mathrm{a})\).
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Chapter 11: Problem 4
Prove that \((0,1]=\bigcap_{n=1}^{\infty}(0,1+1 / n)\), as asserted in Example \(11.1 .6(\mathrm{a})\).
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Show that the set \(\mathbb{Q}\) of rational numbers is neither open nor closed.
Show that \(A=\\{1 / n: n \in \mathbb{N}\\}\) is not a closed set, but that \(A \cup\\{0\\}\) is a closed set.
A point \(x \in \mathbb{R}\) is said to be a boundary point of \(A \subseteq \mathbb{R}\) in case every neighborhood \(V\) of \(x\) contains points in \(A\) and points in \(\mathcal{C}(A)\). Show that a set \(A\) and its complement \(\mathcal{C}(A)\) have exactly the same boundary points.
Show that the set \(\mathbb{N}\) of natural numbers is a closed set.
Show that if \(G\) is an open set and \(F\) is a closed set, then \(G \backslash F\) is an open set and \(F \backslash G\) is a closed set.
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