Set that is not algebraic
39114
Prove that a set in $\mathbb R^3$ is not an algebraic set
4383
Finitely generated monoids - how to show that there is not first order set axiomatizing them.
151719
Connected set in $\mathbb{S}^1$
147459
Find a non-constructible algebraic number of degree $4$ over $\Bbb Q$
100919
Examples of non-measurable sets in $\mathbb{R}$
6675
Lebesgue measurable set that is not a Borel measurable set
132165
"Polynomials" with non-integer exponents
147534
The set of irrational numbers is not a $F_{\sigma}$ set.
49195
How to add mathematical notation of a set
112371
Computing irreducible components of algebraic set
90826
Constructing a subset not in $\mathcal{B}(\mathbb{R})$ explicitly
77112
Artinian rings that are not Artin algebras
3896
A closed set in $(A, \mathcal T_A)$ that is not closed in $(X, \mathcal T)$
78873
How to show that the monomials are not a Schauder basis for $C[0,1]$
110957
No non-trivial clopen sets in $\mathbb{R}$? How to give a direct proof?
125077
what is the absolute value of a set?
49147
Showing that the class of all sets of a particular cardinality is not a set.