cardinality of a countable union

Let $C$ be a countable collection of countable sets. Then $\cup C$ is countable.

Title	cardinality of a countable union
Canonical name	CardinalityOfACountableUnion
Date of creation	2013-03-22 11:59:59
Last modified on	2013-03-22 11:59:59
Owner	vampyr (22)
Last modified by	vampyr (22)
Numerical id	5
Author	vampyr (22)
Entry type	Theorem
Classification	msc 03E10
Related topic	A_nAreCountableSoIsA_1XXA_nIfA_1