Show that $\|.\|_{1/2}$ is not a norm.
91750
$l^p$ not norm, $p<1$
93606
Showing that $C[0,1]$ is not complete
149664
Norm is sup of inner products (proof).
155604
Show that $k[x,y]/(xy-1)$ is not isomorphic to a polynomial ring in one variable.
97391
Prove that $(C^1[0,1], \|\cdot\|)$ is not a Banach space
138459
Norm and Algebraic Integers
25397
Prove $R \times R$ is NOT an integral domain
32917
Show that, for $t>0$, $\log t$ is not a polynomial.
88259
prove that $\frac{1}{x}$ is not uniformly continuous on $(0,1)$
135241
Show that $\mathbb{Z}/n^2\mathbb{Z}$ is not isomorphic to other group
82046
prove that this double transpose $T''$ it's not injective.
17262
Bounded operator that does not attain its norm
35569
Prove that $[0,1]$ isn't homeomorphic to $\mathbb{R}$
148954
Understanding a statement about equivalent norms ($||\cdot ||_2 \sim||\cdot||_1 $)
58329
Show that $y_1$ and $y_2$ are not Linearly Independent
114813
Proof: in $\mathbb{R}$, $((0,1),|\cdot|)$ is not compact.
155974
Show $||Tx||_2 \leq ||(v_n)||_2 \cdot ||x||_{\infty}$