Bourbaki

Proposition 14

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

Algebra, chapter II, § 7. Vector spaces

Given an exact sequence

(23)

0→E′→E→E′′→0 0 \to E' \to E \to E'' \to 0
of right vector spaces over a field K and linear mappings and a left vector space F over K, the corresponding sequence of Z\mathbf{Z}-linear mappings
0→E′⊗KF→E⊗KF→E′′⊗KF→0 0 \to E' \otimes_K F \to E \otimes_K F \to E'' \otimes_K F \to 0
is exact and splits.

As the sequence (23) splits, this is a particular case of § 3, no. 7, Corollary 5 to Proposition 7 and § 3, no. 6, Proposition 5.

Because of Proposition 14, when E′E' is a vector subspace of EE, j:E′→Ej : E' \to E the canonical injection, E′⊗KFE' \otimes_K F is usually identified with a sub-Z\mathbf{Z}-module of E⊗KFE \otimes_K F by means of the injection j⊗1Fj \otimes 1_F. With this convention:

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

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Cites

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