Bourbaki

Definition 1

Tag 0A4H, permanent. Cite it as [Bourbaki, Tag 0A4H].

Lie Groups and Lie Algebras, chapter II, § 4. Central filtrations

Let GG be a group. A real filtration on GG is a family (Gα)α∈R(G_\alpha)_{\alpha \in \mathbf{R}} of subgroups of GG such that

Gα=⋂β<αGβfor all α∈R. G_\alpha = \bigcap_{\beta < \alpha} G_\beta \quad \text{for all } \alpha \in \mathbf{R}.

Formula (1) implies Gα⊂GβG_\alpha \subset G_\beta for β<α\beta < \alpha and hence the family (Gα)(G_\alpha) is decreasing. The filtration (Gα)(G_\alpha) is called separated if ⋂αGα\bigcap_\alpha G_\alpha reduces to the identity element and is called exhaustive if G=⋃αGαG = \bigcup_\alpha G_\alpha.

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 volume. Not translated.