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Let $x$ and $y$ be unique real numbers. How do you prove that there exists a neighborhood $P$ of $x$ and a neighborhood $Q$ of $y$ such that $P \cap Q = \emptyset$?

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    **Hint:** Consider $d = \dfrac{|x - y|}{2}$.2012-09-03
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    One usually writes "Let $x$ and $y$ be distinct real numbers."2012-09-04

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