Partial orders on conjugacy classes in the Weyl group and on unipotent conjugacy classes

Let $G$ be a reductive group over an algebraically closed field and let $W$ be its Weyl group. In a series of papers, Lusztig introduced a map from the set $[W]$ of conjugacy classes of $W$ to the set $[G_u]$ of unipotent classes of $G$. This map, when restricted to the set of elliptic conjugacy classes $[W_e]$ of $W$, is injective. In this paper, we show that Lusztig’s map $[W_e] \to [G_u]$isorder-reversing,withrespecttothenaturalpartialorderon$[W_e]$arisingfromcombinatoricsandthenaturalpartialorderon$[G_u]$ arising from geometry.