Proving that $S_k = \{A \subset \mathbb{N} : |A| = k\}$ for $k\in\mathbb{N}$ is denumerable.
60359
Proving that these two sets are denumerable.
120273
Showing that a collection of sets is a $\sigma$-algebra: either set or complement is countable
103106
Proving that any permutation in $S_n$ can be written as a product of disjoint cycles
131983
Prove that $A \subset B$ if and only if $A \setminus B = \emptyset$
105221
Confusion about Satisfiability by a denumerable sequence.
144787
Show that the set of all infinite subsets of $\mathbb{N}$ has cardinality greater than $\mathbb{N}$
9522
Proving $k \binom{n}{k} = n \binom{n-1}{k-1}$
50880
Expressing $\Bbb N$ as an infinite union of disjoint infinite subsets.
115782
Proof $\mathbb{A}^n$ is irreducible, without Nullstellensatz
99782
$a_{n+1}=|a_n|-a_{n-1} \implies a_n \; \text{is periodic}$
142993
Proof of A ⊆ C and B ⊆ C ⇔ A ∪ B ⊆ C
80916
How to prove that if $A\subseteq A\times A$, then $A=\varnothing$?
127843
Prove that, for any natural number $k$ $\exists m \in M $ s.t i) $m$ has exactly $k$ $1$'s, an
91947
Proof of $ f:I_n \rightarrow I_m \Rightarrow n = m$
54406
Is $\mathbb Q \times \mathbb Q $ a denumerable set?
104855
Prove that $N \subset Z(G)$
21114
$S=\{(n,{1\over n}):n\in\mathbb{N}\}$ is closed in $X$?