Why has $\pi$ to be surjective in the definition of the quotient topology?
40415
Why do we require quotient to be surjective?
120345
Topology induced by seminorms and initial topology
12104
How to prove this result involving the quotient maps and connectedness?
37058
Induced maps in homology are injective
45991
Why $f\colon \mathbb{Z}_n^\times \to \mathbb{Z}_m^\times$ is surjective?
53168
Surjective, Injective, Bijective Functions from $\mathbb Z$ to itself
41872
Show that $\mathbb{R}^2$ is not homeomorphic to $\mathbb{R}^2 \setminus\{(0,0)\}$
142652
When is the product of two quotient maps a quotient map?
72115
Why isn't there a continuously differentiable surjection from $I \to I \times I$?
98971
Why is $\pi r^2$ the surface of a circle
129452
Groups $G,H$ with surjective homomorphisms that are quotient of each other
72190
Topological proof on discrete topology where $X$ is infinite
61794
Interesting and unexpected applications of $\pi$
152297
Understanding quotients of $\mathbb{Q}[x]$
125761
Is this proof for Theorem 16.4 Munkres Topology correct?
84114
Does there exist a surjective homomorphism from $(\mathbb R,+)$ to $(\mathbb Q,+)$ ?
46748
If $g \circ f$ is surjective, show that $f$ does not have to be surjective?