Covering map implies local homeomorphism

From Topospaces

Statement

Suppose and are topological spaces and is a Covering map (?). Then, is a Local homeomorphism (?).

Proof

Given: A covering map . A point .

To prove: There exists an open subset of containing such that the restriction of to is a homeomorphism.

Proof:

Step no. Assertion Definitions used Previous steps used Explanation
1 Let -- --
2 There exists an open subset of such that , a discrete space , and a homeomorphism such that is projection on the first coordinate. covering map (1)
3 Let be the second coordinate of . Let be . Then contains -- (2) By definition, . Since is bijective, we get that .
4 is an open subset of -- (2), (3) Since is a homeomorphism, it suffices to note that is an open subset of . This in turn follows from the fact that being a discrete space, is an open subset of .
5 is an open subset of -- (2), (4) Since is continuous and is open in , is open in . Step (4) says that is open in . Combining, we get that is open in .
6 The restriction of to gives a homeomorphism from to . -- (2)-(5) We have that . Restricted to , the map is the composite of a homeomorphism from to and a projection (homeomorphism) from to . Hence, the map overall is a homeomorphism.