Bourbaki

Exercise 2, § 1

General Topology, X

Let XX be a set, let YY be a Hausdorff uniform space containing more than one point, and let S1,S2\mathscr{S}_1, \mathscr{S}_2 be two sets of subsets of XX which satisfy conditions (FI′),(FII′)(F'_I), (F'_{II}) of no. 2. Show that if S1⊂S2\mathscr{S}_1 \subset \mathscr{S}_2 and S1≠S2\mathscr{S}_1 \neq \mathscr{S}_2, then the uniformity of S1\mathscr{S}_1-convergence is strictly coarser than the uniformity of S2\mathscr{S}_2-convergence. In particular:

(i) If XX is a non-compact Hausdorff topological space, the uniformity of compact convergence is strictly coarser than the uniformity of uniform convergence.

(ii) If XX is a Hausdorff topological space which has infinite compact subsets (cf. Chapter I, § 9, Exercise 4), then the uniformity of pointwise convergence is strictly coarser than the uniformity of compact convergence.

Solution

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Transcribed from the printed volume. Not translated.