Intersection homology of an even-dimensional suspension
= Intersection homology of an even-dimensional suspension
For $\dim L=2n-1$ and <lower middle perversity>, the suspension with two distinct vertices has $IH_i(\operatorname{Susp}L)=IH_i(L)$ for $i<n$, zero for $i=n$, and $IH_{i-1}(L)$ for $i>n$. Cover it by its two open cones. The <Mayer–Vietoris sequence> compares their truncated groups with $IH_*(L)$; below $n$ the overlap map is the injective signed diagonal, and above $n$ both cone groups vanish.