Proof of “The product of two quotient maps need not be a quotient map”
37841
Product of quotient maps and quotient space that is not Hausdorff
69046
Proof of $\mathbb{Q}$ is not cyclic
16548
Prove $(x+y) \text{ mod } n = ((x \text{ mod } n)+(y \text{ mod } n)) \text{ mod } n,\,$ and product analog
84348
Every retraction is a quotient map?
108408
Example of quotient mapping that is not open
121810
Prove that the product of two infinite cyclic groups is not infinite cyclic.
147752
Is the quotient map a homotopy equivalence?
52729
Homotopic maps $(X, A) \to (Y, B)$ induce homotopic maps $X/A \to X/B$
4240
The proof of Triple Vector Products
142174
Nonexistence of an injective $C^1$ map between $\mathbb R^2$ and $\mathbb R$
125668
A proof that BS(1,2) is not polycyclic
62711
Canonical map $R/(I\cap J)\rightarrow R/I\times _{R/(I+J)} R/J$ is an isomorphism
72295
A difficulty in understanding the proof of distributivity of tensor products over direct sums for modules.
139176
The real line is not homeomorphic to any non-trivial product space
115851
Why is this quotient space not Hausdorff?
115606
Proofs involving $ (A\setminus B) \cup (A \cap B)$
44069
Proof that a continuous map to $S^n$ whose image is a proper subset of $S^n$ is null-homotopic