Why is a quotient mapping not necessarily open?
108408
Example of quotient mapping that is not open
148507
Why an open set in $R^n$ might not be written as countable union of disjoint open intervals?
1117
Is there a bijection between $(0,1)$ and $\mathbb{R}$ that preserves rationality?
89264
Connectedness in the Quotient Space
15175
When does a Möbius transformation map $\Im(z)>0$ to itself?
157578
perfect map in topology
147752
Is the quotient map a homotopy equivalence?
152297
Understanding quotients of $\mathbb{Q}[x]$
25874
Showing that a certain map is not flat by explicit counterexample
98696
Is the exponential map ever not injective?
60981
Understanding relation between Quotient Space and $S^1$
63701
An example of a regular function over an open set
92870
composition of covering maps
79424
Don't understand proof that interior of a set is open
148187
Question regarding one-point compactification and homeomorphisms
135126
Proving that the quotient manifold is orientable if and only if the group action is orientation-preserving
40415
Why do we require quotient to be surjective?