Showing that $\{(x,|x|):x\in\mathbb{R}\}$ is not the image of an immersion
96567
Immersion of $\mathbb{R}$ to $\mathbb{R}^2$
79727
Direct proof of non-flatness
131082
Proof that $\mathbb R/[0,1]$ and $\mathbb R$ are homeomorphic
1720
Show that $\langle 2,x \rangle$ is not a principal ideal in $\mathbb Z [x]$
29653
Show that $xy=0$ is a variety but not a manifold
114640
Showing that an ideal is not a free $R-$module.
149095
$f(\mathbb{R}\setminus \mathbb{Q}) \subseteq \mathbb{Q}$ and $f(\mathbb{Q}) \subseteq \mathbb{R}\setminus \mathbb{Q}$ imply that $f$ is not continuous
42774
Examples of involutions on $\mathbb{R}$
84301
Showing that some Function on the Unit Disc is injective
139176
The real line is not homeomorphic to any non-trivial product space
76661
Checking the maximality of a principal ideal in $R[x]$
114813
Proof: in $\mathbb{R}$, $((0,1),|\cdot|)$ is not compact.
78873
How to show that the monomials are not a Schauder basis for $C[0,1]$
85092
Proving $ f(x) = x^2 $ is not uniformly continuous on the real line
131000
A proof of a criterion of vanishing of a function.
2677
Baire: Show that $f\colon \mathbb{R}\to\mathbb{R}$ is a polynomial in an open bounded set
108955
Showing $(\mathbb{Q},+)$ is not isomorphic to $(\mathbb{R},+)$