For $\mathbb{N}$ a structure in $\mathcal{L}=\{s, 0, 1\}$, are the sum and product definable?
113342
Confusion of the decidability of $(N,s)$
9651
Cardinality of cartesian product of an infinite set with N
5996
Are $(\mathbb{R},+)$ and $(\mathbb{C},+)$ isomorphic as additive groups?
71489
Countable product of Polish spaces
21114
$S=\{(n,{1\over n}):n\in\mathbb{N}\}$ is closed in $X$?
47670
Algebraic proof of $\sum_{i=0}^k{{n \choose i}{m \choose {k-i}}}= {{m+n}\choose k}$
155777
Show that infinite Cartesian product is uncountable
78225
Countable additivity implies countable subadditivity?
42810
Is $(\mathbb{Q},+)$ isomorphic to $(\mathbb{Q}^n,+)$?
72420
Is $\mathbb{N}$ impossible to pin down?
10211
Proving that $\sum\limits_{k=0}^{n} {{m+k} \choose{m}} = { m+n+1 \choose m+1 }$
133266
If $(X, \mathcal{T})$ has a countable subbasis, then it has a countable basis
136321
Show that if $\sup\big\{\sum\lvert\, f(a)\rvert\big\}  0\}$ is countable.
143069
What are the direct summands in $\mathbb{Z}^n$?
34520
Is $0\,\mathrm{m}$ dimensionless?
62504
Is there any known relationship between $\sum_{i=1}^{n} f(i)$ and $\sum_{i=1}^{n} \dfrac {1}{f(i)}$
59724
Proving that $x_n\to L$ implies $|x_n|\to |L|$, and what about the converse?