Baire category theorem : Rationals
7607
How to prove that $\mathbb{Q}$ is not the intersection of a countable collection of open sets.
85895
Proving all rational numbers including negatives are countable
78412
Representing a countable field by $\Bbb N$ [transport of algebraic structure]
43711
Categorical Quotient and group actions
138768
Showing that the family of Borel sets is countably generated
141114
Question about a bijection between $\mathbb R$ and $\mathbb R \cup \{\infty\}$
53531
Birational and faithfully flat $\implies$ isomorphism
102899
Category theory with objects as logical expressions over $\{\vee,\wedge,\neg\}$ and morphisms as?
115502
Analogue of the Cantor-Bernstein-Schroeder theorem for general algebraic structures
127886
Artin's lemma and some morphisms.
63574
small limits in the pointed category of a category with all small limits
6904
questions about extremal epimorphisms in category theory
42412
Singular homology $S^{n}$ with rational coefficients
48804
Enumeration of rationals from Stein-Shakarchi's Real Analysis (Chapter 1, Exercise 24)
122559
Some questions on abelian category
5803
Produce an explicit bijection between rationals and naturals?
108305
How can we show that the dyadic rationals are dense in $\mathbb R$?