Combinatorial proof by demonstrating bijection
71534
Combinatorial explanation for why $n^2 = {n \choose 2} + {n+1 \choose 2}$
70282
Help finding a combinatorial proof of $k {n \choose k } = n {n - 1 \choose k -1}$
67927
Combinatorial argument for the identity $k\binom{n}{k} = n\binom{n-1}{k-1}$
33104
Combinatorial Proof with Summation Identity
67451
Building a bijection from a finite union of countable sets to $\mathbb{N}$
65983
Combinatorial proof of binomial coefficient summation identity
36388
How to derive this Combinatorial identity
21391
Proving Functions are Surjective
23125
Prove that there is a bijection between the set of all subsets of $X$, $P(X)$, and the set of functions from $X$ to $\{0,1\}$.
21663
Bijection between power sets of sets implies bijection between sets?
61483
Prove the following identity combinatorially
29828
Combinatorial proof of $\sum^{n}_{i=1}\binom{n}{i}i=n2^{n-1}$.
93964
Proving that $f$ is a bijection from $N$x$N$ to $N$.
92784
Intuitive (combinatorial) proof of $2^n=\sum_{k=0}^n {n\choose k}$
107964
Simple combinatorics problem.
130381
bijection from $(a,b)$ to $\Bbb R$
26343
Number of certain (0,1)-matrices, Stanley's Enumerative Combinatorics