Events

DMS Combinatorics Seminar

Time: Feb 25, 2026 (01:00 PM)
Location: 328 Parker Hall

Details:

donggyu

Speaker: Donggyu Kim, (Georgia Institute of Technology) 

Title: Pseudo-orientable ribbon graphs

 

As consequences, we obtain the Matrix--Quasi-tree Theorem for pseudo-orientable ribbon graphs and the log-concavity on a sequence \(q_i\) counting quasi-trees of size \(2i-1\) or \(2i\). To prove the latter result, we generalize Stanley's log-concavity theorem for regular matroids to regular \(\Delta\)-matroids. Finally, we exhibit an infinite family of non-pseudo-orientable ribbon graphs that fail to satisfy log-concavity.

This is joint work with Changxin Ding.