Bourbaki

Theorem 2

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

General Topology, chapter V, § 3. Topological characterization of the groups R and T

A connected group GG in which there exists a neighbourhood of the identity element homeomorphic to an open interval of R\mathbf{R} is isomorphic to either R\mathbf{R} or T\mathbf{T}.

This is an immediate consequence of the preceding theorem, together with Proposition 7 of § 1, no. 4.

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 volume. Not translated.