All combinatorial derangements of $1,2,3 \cdots k$ with specified rules
97314
Counting nearly-sorted permutations
3786
Help finding a combinatorial proof of $k {n \choose k } = n {n - 1 \choose k -1}\;$
18634
Combinations of sets raised to the power of a prime modulus: $\binom{p^{\alpha}-1}k \equiv (-1)^k \pmod p$
1139
Combinatorial proof of $\sum_{j=0}^{k} \binom{n}{j} = \sum_{j=0}^k \binom{n-1-j}{k-j}2^j$
81505
Derangement of $n$ elements
67927
Combinatorial argument for the identity $k\binom{n}{k} = n\binom{n-1}{k-1}$
111032
Proof of Sets involving the Cartesian Product
5183
Divisibility of determinant.
151520
About the parity of the product $(a_1-1)(a_2-2)\cdots(a_n-n)$
74730
Combinatorial Proof of ${{n}\choose{k}} {{k}\choose{j}} = {{n}\choose{j}} {{n-j}\choose{k-j}}$
153072
Guessing a subset of $\{1,...,N\}$
126025
Computing the inverse of a permutation
12459
Associativity of symmetric difference of sets
39953
$a\mid b,\ c\mid d\,\Rightarrow\ ac\mid bd $ $\ \, \bf\small [Divisibility\ Product\ Rule]$
5801
Combinatorial proof help
62175
A general formula for $n$ distinguishable arrangements of length $\ell$ of a sequence of a given size?
35666
How to prove the divisibility rule for $3\, $ [casting out threes]