!!! Overview
[{$pagename}] also called an identity relation or identity map or identity transformation, is a [function] that always returns the same value that was used as its argument. 

In equations, the function is given by f(x) = x.


Formally, if M is a set, the [{$pagename}] f on M is defined to be that function with domain and codomain M which satisfies

f(x) = x   for all elements x in M.

In other words, the function value f(x) in M  is always the same input element x of M .

!! More Information
There might be more information for this subject on one of the following:
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* [#1] - [Identity_function|Wikipedia:Identity_function|target='_blank'] - based on information obtained 2018-01-10-