Bourbaki

Corollary 1

Tag 06T0, permanent. Cite it as [Bourbaki, Tag 06T0].

Algebra, chapter V, § 14. Transcendental extensions

— Suppose that E is a finitely generated extension of K, and let K′K' be the relative algebraic closure of K in E (V, p. 19). Then K′K' is of finite degree over K.

Let B be a transcendence basis of E over K. By Cor. 2 of V, p. 114, K′K' is linearly disjoint from K(B)K(B) over K, whence [K′:K]=[K′(B):K(B)]≤[E:K(B)][K' : K] = [K'(B) : K(B)] \leq [E : K(B)] and now the finiteness of [K′:K][K' : K] follows from that of [E:K(B)][E : K(B)].

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.