Definition 4

Tag 05WR, permanent. Cite it as [Bourbaki, Tag 05WR].

Algebra, chapter II, § 10. Matrices

A matrix whose rows and columns have the same indexing set is called a square matrix.

A square matrix with $n$ rows and $n$ columns is called a matrix of order $n$ .

Bourbaki puts the proof directly after the statement, so what is above is the statement and its proof together.

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