===== Binary operation =====
==== Set ====
| @#55CCEE: context     | @#55CCEE: $X$ |
| @#FF9944: definition  | @#FF9944: it $\equiv X\times X\to X$ | 

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=== Discussion ===
Also called "law of composition".

It's is a binary function with which takes elements of $X$ to an element of $X$ itself.

=== Reference ===
Wikipedia: [[http://en.wikipedia.org/wiki/Binary_operation|Binary operation]]

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=== Subset of ===
[[Binary function]]
=== Equivalent to ===
[[Magma]]