Bourbaki

Proposition 6

Tag 0633, permanent. Cite it as [Bourbaki, Tag 0633].

Algebra, chapter III, § 7. Exterior algebras

If M is a finitely generated A-module, ⋀(M)\bigwedge(M) is a finitely generated A-module; also, if M admits a generating system with n elements, then ⋀p(M)={0}\bigwedge^p(M) = \{0\} for p>np > n.

Let (xi)1≤i≤n(x_i)_{1 \leq i \leq n} be a generating system of M. Every element of ⋀p(M)\bigwedge^p(M) is a linear combination of elements of the form

xi1∧xi2∧⋯∧xip x_{i_1} \wedge x_{i_2} \wedge \cdots \wedge x_{i_p}
where the indices iki_k belong to {1,n}\{1, n\}; by Proposition 5, these indices can be assumed to be distinct (otherwise the corresponding element is zero). If p>np > n, there is no such sequence of indices and hence ⋀p(M)={0}\bigwedge^p(M) = \{0\}. If p≤np \leq n, these sequences are finite in number, which completes the proof.

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

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Transcribed from the printed edition, 1998, Springer. Not translated.