Shellability of uncrossing posets and the CW poset property
Patricia Hersh (North Carolina State University)
MSRI: Simons Auditorium
Matthew Dyer’s proof that reflection orders give rise to EL-shellings for Bruhat order relied on the fact that the number of so-called ascending chains in a closed interval in Bruhat order is the leading coefficient in a polynomial closely related to the Kazhdan– Lusztig polynomial. We give a new, poset-theoretic proof that reflection orders yield EL-shellings for Bruhat order based on a characterization of cover relations in Bruhat order which may not be so well known. This perspective also enables us to prove a conjecture of Thomas Lam that face posets of stratified spaces of response matrices of electrical networks are dual EL-shellable and are CW posets.