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Topological manifolds are locally compact and locally path connected
Statement
Every topological manifold is locally compact and locally path connected. More precisely, every point has a neighbourhood basis consisting of open sets whose closures are compact and which are path connected.
Facts & Assumptions
Given: A topological manifold and a point .
Every neighbourhood of contains a coordinate ball whose closure is compact (Coordinate balls form a basis of a topological manifold).
For , every Euclidean open ball is path connected and every neighbourhood in contains a path-connected open ball ( is polygonally connected, connected, locally path-connected and locally connected).
For , Euclidean space is locally compact ( is locally compact and -compact).
Homeomorphisms preserve path connectedness and compactness.
Proof
Let be any open neighbourhood of . By [F1] choose a chart [F1, choose] at and an open Euclidean ball such that and the closure of in is compact. This already gives a compact neighbourhood basis at , so is locally compact.
If the manifold dimension is , then every point is open, so is [L1, A1, step 1.1] locally path connected trivially. If , then [L1] says the Euclidean ball is path connected. Since is a homeomorphism on , [A1] makes path connected. Thus every neighbourhood of contains an open path-connected neighbourhood of .
Step 1.1 proves local compactness and step 2.1 proves local path [step 1.1, step 2.1, L2] connectedness. The role of [L2] is only to justify that the compact-neighbourhood conclusion in step 1.1 matches the Euclidean local model used to produce the coordinate balls.
Depends on
Used by
- A nonzero-degree map to a connected manifold is surjective Corollary
- Bonnet-Myers fundamental group is finite Corollary
- Every Riemann surface is a quotient of a simply connected model Corollary
- Pontryagin numbers of a closed oriented manifold Definition
- Spherical, parabolic and hyperbolic universal-covering types Definition
- Stiefel-Whitney numbers of a closed manifold Definition
- Arcs joining two points of a connected submanifold avoiding finitely many points Lemma
- Embedded bands joining two framed spheres exist Lemma
- Green's second identity on a compact bordered domain of a Riemann surface Lemma
- Harmonic conjugates and integral logarithmic-pole monodromy on surfaces Lemma
- Local slice for a free proper action Lemma
- Regular exhaustion and Dirichlet solutions on relatively compact surface domains Lemma
- The covering of a leaf associated with the holonomy kernel exists Lemma
- The diagonal and graph classes contract to the alternating trace Lemma
- The fundamental-group label controls contractibility of the Whitney circle Lemma
- The orientation double cover is canonically oriented and preserves closedness Lemma
- Two points avoiding a finite set lie in a common embedded ball Lemma
- Components of a topological manifold are open and at most countable Proposition
- The quotient foliation under a free and properly discontinuous foliated action Proposition
- Cartan hadamard Theorem
- Degree of a proper holomorphic map of Riemann surfaces Theorem
- Free proper action quotient manifold Theorem
- Positive smooth densities give Radon volume Theorem
- Topological manifolds are metrizable and paracompact Theorem
- Universal covering Lie group Theorem
Dependency tree · two levels
16 results within two dependency steps of this one, each drawn at its shortest distance from it. An arrow runs from a result to what uses it, so the chart reads left to right and ends at this result, which carries a heavier outline. Every node is a link to that result. Click elsewhere on the chart to enlarge it.
Sources
- Rob van der Vorst, Introduction to differentiable manifolds, §1 (standard reference, not scraped)
- Nigel Hitchin, Differentiable Manifolds, §2.2 (standard reference, not scraped)