Bourbaki

Proposition 16

Tag 0B93, permanent. Cite it as [Bourbaki, Tag 0B93].

General Topology, chapter I, § 9. Compact spaces and locally compact spaces

Every closed subspace FF of a paracompact space XX is paracompact.

Certainly FF is Hausdorff. On the other hand, if (Vi)(V_i) is an open covering in the subspace FF, then each ViV_i is of the form Vi=Ui∩FV_i = U_i \cap F, where UiU_i is open in XX. Consider the open covering R\mathscr{R} of XX formed by CFCF and the UiU_i; since XX is paracompact, R\mathscr{R} has a locally finite refinement R′\mathscr{R}', and the intersections with FF of the sets belonging to R′\mathscr{R}' form a locally finite open covering of FF which is finer than the given covering (Vi)(V_i).

On the other hand an open subspace of a compact space need not be paracompact (Exercise 11).

Bourbaki puts the proof directly after the statement, so what is above is the statement and its proof together.

Cited by

Cites

Transcribed from the printed volume. Not translated.