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Research seminar in Discrete Mathematics
Sunflowers and Ramsey problems for restricted intersections
Sunflowers and Ramsey problems for restricted intersections
Organizers
Jie Ma
, Benjamin Sudakov
Speaker
Barnabas Janzer
Time
Tuesday, March 10, 2026 5:05 PM - 6:15 PM
Venue
Online
Online
Zoom 787 662 9899
(BIMSA)
Abstract
Extremal problems on set systems with restricted intersections have been an important part of combinatorics in the last 70 years. For many of the known results, one of the fundamental tools used is Füredi’s celebrated semilattice lemma, which is a key ingredient in the powerful delta-system method. Motivated by a Ramsey-type problem for restricted intersections, we study the quantitative dependence in Füredi’s result, and prove that one cannot remove the double-exponential dependency on the uniformity. However, we provide an alternative with significantly better, single-exponential dependency on the parameters, which is still strong enough for most applications of the delta-system method. Joint work with Zhihan Jin, Benny Sudakov and Kewen Wu.