Bourbaki

Remark

Tag 0DJ9, permanent. Cite it as [Bourbaki, Tag 0DJ9].

Algebra, chapter IX, § 1. Formes sesquilinéaires

Let A be a ring endowed with an antiautomorphism J, M and N right A-modules, and Φ\Phi a left sesquilinear form for J on M×NM \times N (No. 2, Remark); it therefore satisfies the equality

Φ(xa,xa′)=ajΦ(x,y)a′(a,a′∈A,x∈M,y∈N). \Phi(xa, xa') = a^j \Phi(x, y)a' \quad (a, a' \in A, x \in M, y \in N).

The mapping Φ′\Phi' of N×MN \times M into A defined by Φ′(y,x)=Φ(x,y)J′\Phi'(y, x) = \Phi(x, y)^{J'} (where J′=J−1J' = J^{-1}) is a left sesquilinear form for J′J', and Φ\Phi and Φ′\Phi' identify with bilinear forms on MJ′×NM^{J'} \times N and NJ′×MN^{J'} \times M respectively. The mappings sΦs_\Phi and sΦ′s_{\Phi'} associated with these bilinear forms are called the left and right associated mappings to the sesquilinear form Φ\Phi, and are denoted by sΦs_\Phi and dΦd_\Phi. Thus, by definition

(26)(26)
Φ(x,y)=⟨y,sΦ(x)⟩=⟨x,dΦ(y)⟩j(x∈M,y∈N), \Phi(x, y) = \langle y, s_\Phi(x) \rangle = \langle x, d_\Phi(y) \rangle^j \quad (x \in M, y \in N),

and sΦs_\Phi (resp. dΦd_\Phi) is a linear mapping of MJ′M^{J'} into N∗N^* (resp.

of N′N' into M∗M^*). One would state and prove easily the analogues, for the case considered here, of Definition 7 and of props. 4, 5, 6.

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

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