Bourbaki

Corollary 2

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

Algebra, chapter V, § 9. Conjugate elements and quasi-Galois extensions

— Let E and F be two algebraic extensions of K such that E⊂FE \subset F. If F is quasi-Galois over K, then it is quasi-Galois over E.

We may assume that F⊂ΩF \subset \Omega. Let uu be an E-automorphism of Ω\Omega. Since uu is a K-automorphism of Ω\Omega and F is quasi-Galois over K, we have u(F)=Fu(F) = F, therefore F is quasi-Galois over E.

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

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Cites

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Transcribed from the printed edition, 2003, Springer. Not translated.