# Countable set/Related Articles

From Citizendium, the Citizens' Compendium

*See also changes related to Countable set, or pages that link to Countable set or to this page or whose text contains "Countable set".*

## Parent topics

- Cardinality [r]: The size, i.e., the number of elements, of a (possibly infinite) set.
^{[e]} - Set (mathematics) [r]: Informally, any collection of distinct elements.
^{[e]} - Set theory [r]: Mathematical theory that models collections of (mathematical) objects and studies their properties.
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## Subtopics

- Infinity [r]:
*Add brief definition or description* - Natural number [r]: An element of 1, 2, 3, 4, ..., often also including 0.
^{[e]} - Galileo's paradox [r]: The observation that there are fewer perfect squares than natural numbers but also equally many.
^{[e]} - Hilbert's hotel [r]: A fictional story which illustrates certain properties of infinite sets.
^{[e]} - Cantor's diagonal argument [r]: Proof due to Georg Cantor showing that there are uncountably many sets of natural numbers.
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