## Knuth (2000) Dancing Link

A paper that is easy to read, summarizing the development of algorithm to set cover problem. The name “dancing link” is how Knuth called his implementation of depth-first-search. Wikipedia has an article about that, named Knuth’s Algorithm X. [more]

## Permutation and cycles

Let $[n]$ be the set ${1,2,…,n}$ (we call each element a vertex) and a permutation of $[n]$ be $\pi=[\pi(1),\pi(2),\cdots,\pi(n)]$, i.e., denote $\pi(x)=y$ the fact that in a permutation, position $x$ has vertex $y$. There are $n!$ possible permutations of $[n]$. [more]