How to prove that the set of rational numbers are countable?
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How to prove that $\mathbb{Q}$ ( the rationals) is a countable set
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Existence in ZF of a set with countable power set
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What is wrong with this proof that the power set of natural numbers is countable?
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Prove that the union of countably many countable sets is countable.
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The cardinality of the set of countably infinite subsets of an infinite set
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countably infinite union of countably infinite sets is countable
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Subset of a countable set is itself countable
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Let $X$ and $Y$ be countable sets. Then $X\cup Y$ is countable
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How to prove that a set is invariant?
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Proof that every repeating decimal is rational
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Relation on countable sets
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The Cartesian product of a finite number of countable sets is countable
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Example of a set $S$ that is countable, but the set of limit points is uncountable
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Show that the set of functions $\mathbb{N}\to\{0,1\}$ is not countable
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Let S be the set of all real numbers in the interval (0; 1) whose decimal expansions contain only 0's, 4's and 8's. Prove that S is uncountable.
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Real Analysis - Prove a set is countable
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Proof that a perfect set is uncountable