\( \definecolor{colordef}{RGB}{249,49,84} \definecolor{colorprop}{RGB}{18,102,241} \)
Re-prove that \(\mathbb{Z}\) is closed in \(\mathbb{R}\) using the « complement is open » characterization (Exercise on \(\mathbb{Z}\) above already established this through the closure computation; here we revisit it from a different angle).
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