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Texas A&M University

Algebra and Combinatorics Seminar

Date: February 2, 2024

Time: 3:00PM - 4:00PM

Location: BLOC 302

Speaker: Youngho Yoo, TAMU


Title: Minimum degree conditions for apex-outerplanar minors

Abstract: Motivated by Hadwiger's conjecture, we study graphs H for which every graph with minimum degree at least |V(H)|-1 contains H as a minor. We prove that a large class of apex-outerplanar graphs satisfies this property. Our result gives the first examples of such graphs whose vertex cover numbers are significantly larger than a half of its vertices, and recovers all known such graphs that have arbitrarily large maximum degree. Our proof can be adapted to directed graphs to show that every directed graph with minimum out-degree at least t contains a certain orientation of the wheel and of every apex-tree on t+1 vertices as a subdivision and a butterfly minor respectively. Joint work with Chun-Hung Liu.