Inversion (in combinatorics)

Inversion may refer to:

• An inversion of a permutation $\pi$ on the ordered set $\{1,2,\ldots,n\}$ is a pair $i < j$ such that $\pi(i) > \pi(j)$
• A transposition, a permutation that exchanges two elements
• A derangement, a permutation with no fixed points