$\mathbb{Z}[\sqrt{-7}]$ is not an Euclidian Domain
112043
Show that the ideal $ (2, 1 + \sqrt{-7} ) $ in $ \mathbb{Z} [\sqrt{-7} ] $ is not principal
121986
Do the Laurent polynomials over $\mathbb{Z}$ form a principal ideal domain?
14003
$(\mathbb{Z}/2^n \mathbb{Z})^*$ is not cyclic Group for $n\geq 3$
72144
Show that $\mathbb Q(\sqrt p) \not\simeq\mathbb Q(\sqrt q)$
70576
Elementary proof that $\mathbb{R}^n$ is not homeomorphic to $\mathbb{R}^m$
108955
Showing $(\mathbb{Q},+)$ is not isomorphic to $(\mathbb{R},+)$
137285
Prove $\mathbb{Z}_2 \times \mathbb{Z}_2$ is not isomorphic to $\mathbb{Z}_4$
58717
Why isn't $\mathbb Z [\sqrt{pq}]$ a factorial domain
93621
Prove that $\mathbb{Z}[\omega]$ is an integral domain
23048
The ring $\mathbb Z[\sqrt{-2}]= \{a+b\sqrt{-2} ; a\in \mathbb Z,b\in \mathbb Z \}$ has a Euclidean algorithm
79056
Prove that $\mathbb Z^n$ is not isomorphic to $\mathbb Z^m$ for $m\neq n$
68838
Why $\sqrt[3]{3}\not\in \mathbb{Q}(\sqrt[3]{2})$?
88474
$\mathbb{A}^{2}$ not isomorphic to affine space minus the origin
94747
Show that the rings $2\mathbb{Z}$ and $3\mathbb{Z}$ are not isomorphic.
158502
Showing $\sin(\bar{z})$ is not analytic at any point of $\mathbb{C}$
104486
Ideal in $\mathbb Z[x]$ which is not two-generated
81982
Is $\mathbb{Z}[x]$ a principal ideal domain?