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.
|