“…On surfaces Hilb k (S ) = GHilb k (S ), and the cohomological intersection theory of Hilb k (S ) can be approached from several different directions: 1) via the inductive recursions set up in [14,15,16]; 2) using Nakajima calculus [39,24,33,20] or more recently 3) virtual localisation on Quot schemes [22,35]. Lehn's conjecture [33] on top Segre numbers of tautological line bundles, and its recent extension, the Segre-Verlinde duality conjectures [36,29,21,37], 1 incapsulate the complexity of this theory. However, these techniques fail at a fundamental level in higher dimensions.…”