Covering map implies local homeomorphism
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. |