===== Square matrix =====
==== Set ====
| @#55CCEE: context     | @#55CCEE: $X$ | 
| @#55CCEE: context     | @#55CCEE: $n\in \mathbb N$ | 
| @#FFBB00: definiendum | @#FFBB00: $ \mathrm{Matrix}(n,X)\equiv \mathrm{Matrix}(n,n,X) $ |

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=== Discussion ===
We write $A_{i,j}\equiv (A_i)_j$

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=== Subset of ===
[[Matrix]]