 Perversity

A traditional perversity is a function $\bar{p}:\{2,3,\dots \}\to \mathbb{Z}$ satisfying $\bar{p}(2)=0$ and $\bar{p}(k+1)-\bar{p}(k)\in \{0,1\}$. It specifies how far chains may meet strata of codimension $k$.