What is the fine-grained topic of the following text: His joint work with L. Chen and L.A. Borisov, in which toric Deligne-Mumford stacks are introduced and their orbifold cohomology calculated, has already been used to resolve a long standing conjecture of Hibi on reflexive polytopes. Only return the topic.
Introduction and calculation of toric Deligne-Mumford stacks' orbifold cohomology in joint mathematical work.