How to show that this set is not algebraic
39114
Prove that a set in $\mathbb R^3$ is not an algebraic set
85870
Show this set is a base for some topology on $\mathbb{Z}$
99656
Prove that the set of all algebraic numbers is countable
81682
Proving the algebraic set corresponding to a polynomial is infinite.
63529
How to show that this set is compact in $\ell^2$
88645
Prove that the additive groups $\mathbb{R}$ and $\mathbb{Q}$ are not isomorphic.
54875
How to prove polynomials with degree $n$ does not form a vector space?
70576
Elementary proof that $\mathbb{R}^n$ is not homeomorphic to $\mathbb{R}^m$
25874
Showing that a certain map is not flat by explicit counterexample
4383
Finitely generated monoids - how to show that there is not first order set axiomatizing them.
156457
Show that $K[x,xy,xy^2,\dots]$ is not Noetherian
132382
Showing a set is nowhere dense in $C([0,1])$
10180
How to prove that this set is closed?
11259
Prove $R\times S$ is not an integral domain
69046
Proof of $\mathbb{Q}$ is not cyclic
146707
Formally show that the set of continuous functions is not measurable
78300
Showing a set is closed other than giving a counterexample?