Bourbaki

Definition 12

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

Algebra, chapter IX, § 1. Formes sesquilinéaires

Given two A-modules E, F and a form Φ\Phi sesquilinear for J on E×FE \times F, the form Φ(m)\Phi_{(m)} sesquilinear for J on (∧mE)×(∧mF)(\wedge^m E) \times (\wedge^m F) characterized by (37) is called the extension of Φ\Phi to the m-th exterior powers.

The notations being those of Def. 12, let us study the mappings associated with Φ(m)\Phi_{(m)}. From formula (24) (No. 6) and (37) we obtain the relations

Φ(m)(x1∧…∧xm,y1∧…∧ym)=det⁡(⟨xi,dΦ(yk)⟩)=det⁡(⟨yi,sΦ(xk)⟩j). \Phi_{(m)}(x_1 \wedge \ldots \wedge x_m, y_1 \wedge \ldots \wedge y_m) = \det(\langle x_i, d_\Phi(y_k) \rangle) = \det(\langle y_i, s_\Phi(x_k) \rangle^j).

We therefore have

sΦ(m)=ks∘(∧msΦ),dΦm=kd∘(∧mdΦ), s_{\Phi(m)} = k_s \circ (\wedge^m s_\Phi), \quad d_{\Phi m} = k_d \circ (\wedge^m d_\Phi),

where ksk_s (resp. kdk_d) denotes the canonical mapping of ∧mF∗\wedge^m F^* into (∧mF)∗(\wedge^m F)^* (resp. of ∧mE∗\wedge^m E^* into (∧mE)∗(\wedge^m E)^*) (cf. Chap. III, § 8, No. 2).

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

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