===== Matrix =====
==== Set ====
| @#55CCEE: context     | @#55CCEE: $X$ ... set | 
| @#55CCEE: context     | @#55CCEE: $n,m\in \mathbb N$ | 
| @#FFBB00: definiendum | @#FFBB00: $ A\in \mathrm{Matrix}(n,m,X) $ |
| @#55EE55: postulate   | @#55EE55: $$ A\in\mathrm{FinSequence}(\mathrm{FinSequence}(X)) $$ |
| @#DDDDDD: range       | @#DDDDDD: $ 1\ge i\ge m$ |
| @#55EE55: postulate   | @#55EE55: $\mathrm{length}(A)=n$ |
| @#55EE55: postulate   | @#55EE55: $\mathrm{length}(A_i)=m$ |

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=== Discussion ===
We write 

$A_{ij}\equiv (A_i)_j$

=== Reference ===
Wikipedia:
[[https://en.wikipedia.org/wiki/Matrix_(mathematics)|Matrix_(mathematics)]]

Mathematica:
[[https://reference.wolfram.com/language/guide/MatrixOperations.html|MatrixOperations]]

Idris:
[[https://github.com/idris-lang/Idris-dev/blob/master/libs/contrib/Data/Matrix.idr|contrib/Data/Matrix.idr]]

Haskell:
[[https://hackage.haskell.org/package/matrix-0.3.5.0/docs/Data-Matrix.html | package/matrix-0.3.5.0/docs/Data-Matrix.html]]

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=== Subset of ===
[[Finite sequence]]