Bourbaki

Exercise 4, § 5

General Topology, I, 128

It is set in small type as supplementary.

Let Γ\Gamma be the group of homeomorphisms of the quotient space TT of R\mathbf{R} consisting of the identity and the homeomorphism induced on TT by the homeomorphism x→1/2+xx \to 1/2 + x of R\mathbf{R} onto itself. Let SS be the equivalence relation "there exists σ∈Γ\sigma \in \Gamma such that y=σ(x)y = \sigma(x)" on TT; SS is both open and closed (Exercise 3). Show that TT has no continuous section with respect to SS, although both TT and T/ST/S are compact, connected and locally connected. Let AA be the canonical image in TT of the interval [0,1/2][0,1/2] of R\mathbf{R}. Show that AA is locally closed in TT but that the quotient space A/SAA/S_A is not homeomorphic to the canonical image of AA in T/ST/S. \*

Solution

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Transcribed from the printed volume. Not translated.