Are $\mathbb{N}$ is isomorphic to $\mathbb{Q}$?
43268
How to prove that the set of rational numbers are countable?
98731
Show that there is no epimorphism from ($\mathbb{Q}$, +) to ($\mathbb{Z}$, +)
38549
$\mathbb{Q}(\sqrt{n}) \cong \mathbb{Q}(\sqrt{m})$ iff $n=m$
66169
Ring of order $n$ is isomorphic to $\Bbb Z/n\Bbb Z$, with $n$ square-free
152662
Proving that any finite cyclic group of order $n$ is isomorphic to $$
154318
Can a field be isomorphic to its subfield?
5699
The number of ring homomorphisms from $\mathbb{Z}_m$ to $\mathbb{Z}_n$
124847
Is the set of surjective functions from $\mathbb{N}$ to $\mathbb{N}$ uncountable?
89415
Number of homomorphisms from $(\mathbb Q^+ , \,\cdot\,)$ to $(\mathbb Z_n , +)$
69046
Proof of $\mathbb{Q}$ is not cyclic
137739
Prove that the group isomorphism $\mathbb{Z}^m \cong \mathbb{Z}^n$ implies that $m = n$
108156
Algebraic closure of $\mathbb{C}(x)$ is isomorphic to $\mathbb{C}$
27670
Group homomorphisms $\mathbb{Q}\to\mathbb{R}$
13761
Automorphisms in $\mathbb{Z}_n$
89167
Cardinality of equivalence relations in $\mathbb{N}$
108955
Showing $(\mathbb{Q},+)$ is not isomorphic to $(\mathbb{R},+)$
124333
A bijection between $\mathbb{N}$ and $\mathbb{P}(\mathbb{N})$?