Bourbaki

Remark

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

General Topology, chapter III, § 2. Subgroups, quotient groups, homomorphisms homogeneous spaces, product groups

Let HH be any subgroup of a topological group GG. For each x∈H‾x \in \overline{H} we have xH‾=xx \overline{H} = x. H‾=H‾\overline{H} = \overline{H}, since translation by xx is a homeomorphism of GG onto GG. In other words, for each x∈H‾x \in \overline{H}, xHxH is dense in H‾\overline{H}. It follows that if HH is not closed, then H‾∩CH\overline{H} \cap CH is dense in H‾\overline{H}.

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.