Bourbaki

Remark 3

Tag 0E2P, permanent. Cite it as [Bourbaki, Tag 0E2P].

Algebra, chapter X, § 9. Complexes de Koszul

Let G be a group and ρ:G→GL(L)\rho : G \to \mathbf{GL}(L) a linear representation of G in a flat A-module L. Then the (En)(\mathscr{E}_n) are exact sequences of linear representations. Suppose L finitely generated projective, and denote by RA(G)R_A(G) the ring of representations of G in finitely generated projective A-modules. It follows from prop. 3 that one has in R_A(G) the relations

∑i=0n(−1)i[Si(L)][Λn−i(L)]=0,n>0. \sum_{i=0}^{n} (-1)^i [\mathbf{S}^i(L)] [\Lambda^{n-i}(L)] = 0 , \quad n > 0 .

If one considers the formal series

s(T)=∑i=0∞[Si(L)]Ti∈RA(G)[[T]], s(T) = \sum_{i=0}^{\infty} [\mathbf{S}^i(L)] T^i \in R_A(G)[[T]] ,
λ(T)=∑i=0∞[Λi(L)]Ti∈RA(G)[[T]], \lambda(T) = \sum_{i=0}^{\infty} [\Lambda^i(L)] T^i \in R_A(G)[[T]] ,

the relations (10) are written

s(T)λ(−T)=1∗. s(T) \lambda(-T) = 1_* .

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

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