Bourbaki

Corollary 1

Tag 01IJ, permanent. Cite it as [Bourbaki, Tag 01IJ].

Lie Groups and Lie Algebras, chapter IX, Appendix 1. Structure of compact groups

Let V be a neighbourhood of the identity element of G. Then V contains a closed normal subgroup H of G such that the quotient G/HG/H is a Lie group.

Let (Kλ)λ∈L(K_{\lambda})_{\lambda\in L} be a family of compact Lie groups such that G can be identified with a closed subgroup of ∏λ∈LKλ\prod_{\lambda\in L}K_{\lambda}; for λ∈L\lambda \in L, demote by pλ:G→Kλp_{\lambda}: G\rightarrow K_{\lambda} the restriction to G of the canonical projection. There exists a finite subset J⊂LJ\subset L, and for each λ∈J\lambda \in J a neighbourhood VλV_{\lambda} of the origin in KλK_{\lambda}, such that V contains ⋂λ∈Jpλ−1(Vλ)\bigcap_{\lambda\in J}p^{-1}_{\lambda}(V_{\lambda}). It now suffices to put H=⋂λ∈JH =\bigcap_{\lambda\in J} Ker(pλp_{\lambda}).

Denote by (Hα)α∈I(H_{\alpha})_{\alpha\in I} the decreasing filtered family of closed normal subgroups of G, such that the quotient G/HαG/H_{\alpha} is a Lie group. Consider the projective system of compact Lie groups G/HαG/H_{\alpha} (cf. General Topology, Chap. III, §7, no. 2, Prop. 2).

Bourbaki sets the proof directly after the statement, and the corpus does not separate them, so what is above is the statement and its proof together.

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Cites

  • General Topology, Chap. III, §7, no. 2, Prop. 2 not in this corpus
Transcribed from the printed volume. Not translated.