Local homeomorphism

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Let [ilmath](X,\mathcal{ J })[/ilmath] and [ilmath](Y,\mathcal{ K })[/ilmath] be topological spaces and let [ilmath]f:X\rightarrow Y[/ilmath] be a map (we do not require continuity at this stage). We call [ilmath]f[/ilmath] a local homeomorphism if[1]:

  • [ilmath]\forall x\in X\exists U\in\mathcal{O}(x,X)\big[\big(f(U)\in\mathcal{K}\big)\wedge \big(f\vert_U^\text{Im}:U\rightarrow f(U)\text{ is a } [/ilmath][ilmath]\text{homeomorphism} [/ilmath][ilmath]\big)\big][/ilmath][Note 1]
    • In words: for all points [ilmath]x\in X[/ilmath] there exists open neighbourhoods of [ilmath]x[/ilmath], say [ilmath]U[/ilmath], that [ilmath]f(U)[/ilmath] is open in [ilmath]Y[/ilmath] and [ilmath]f[/ilmath] restricted to [ilmath]U[/ilmath] (onto the image of [ilmath]U[/ilmath]) is a homeomorphism (when [ilmath]U[/ilmath] and [ilmath]f(U)[/ilmath] are considered with the subspace topology of course)

If there is a local homeomorphism between two spaces we say they are locally homeomorphic

Immediate properties

TODO: I do not know if local homeomorphism is preserved by anything, or an equivalence relation
- investigate this. Alec (talk) 21:45, 22 February 2017 (UTC)


  1. Note about notation:


  1. Introduction to Topological Manifolds - John M. Lee