Bourbaki

Corollary

Tag 06DT, permanent. Cite it as [Bourbaki, Tag 06DT].

Algebra, chapter IV, § 5. Symmetric tensors and polynomial mappings

— Assume that A is an infinite integral domain; let M be a free A-module and N a torsion-free A-module.

(i) We have Pol(M,N)=⨁q≥0Polq(M,N)\mathrm{Pol}(M, N) = \bigoplus_{q \geq 0} \mathrm{Pol}^q(M, N) and each Polq(M,N)\mathrm{Pol}^q(M, N) may be identified canonically with Hom(TSq(M),N)\mathrm{Hom}(\mathbf{T S}^q(M), N).

(ii) Let f∈Pol(M,N)f \in \mathrm{Pol}(M, N) and (ei)i(e_i)_i, a basis of M. There exists one and only one family (uν)ν∈N(I)(u_\nu)_{\nu \in N^{(I)}} of elements of N such that f(∑i∈Iλiei)=∑ν∈N(I)λνuνf \left( \sum_{i \in I} \lambda_i e_i \right) = \sum_{\nu \in N^{(I)}} \lambda^\nu u_\nu for all (λi)∈A(I)(\lambda_i) \in A^{(I)}.

The assertion (i) follows from Prop. 16 and 19, and (ii) follows from (i) and the Cor. of Prop. 16.

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, 2003, Springer. Not translated.