Bourbaki

Corollary 3

Tag 06F8, permanent. Cite it as [Bourbaki, Tag 06F8].

Algebra, chapter IV, § 6. Symmetric functions

— For every λ∈A\lambda \in A we have

res⁡p,1(f,λ−X)=f(λ),res⁡1,q(X−λ,g)=g(λ). \operatorname{res}_{p,1}(f, \lambda - X) = f(\lambda), \quad \operatorname{res}_{1,q}(X - \lambda, g) = g(\lambda).
When f(X)=X−λf(X) = X - \lambda, the algebra E is equal to A and we have x=Ax = A; the second formula (32) now follows from Prop. 7 (IV, p. 77). By remarks 1 and 3 (IV, p. 76, 77) we conclude
res⁡p,1(f,λ−X)=(−1)pres⁡1,p(λ−X,f)=(−1)p+pres⁡1,p(X−A,f)=f(A). \operatorname{res}_{p,1}(f, \lambda - X) = (-1)^p \operatorname{res}_{1,p}(\lambda - X, f) = (-1)^{p+p} \operatorname{res}_{1,p}(X - A, f) = f(A).

Suppose now that f and g are monic. We denote by F the A-algebra A[X,Y]/(f(X),g(Y))A[X, Y]/(f(X), g(Y)) and denote by x (resp. y) the canonical image of X (resp. Y) in F.

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.