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PRODID:-//Discrete Mathematics Group - ECPv6.15.20//NONSGML v1.0//EN
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X-ORIGINAL-URL:https://dimag.ibs.re.kr
X-WR-CALDESC:Events for Discrete Mathematics Group
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TZID:Asia/Seoul
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TZOFFSETFROM:+0900
TZOFFSETTO:+0900
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DTSTART:20250101T000000
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BEGIN:VEVENT
DTSTART;TZID=Asia/Seoul:20260407T163000
DTEND;TZID=Asia/Seoul:20260407T173000
DTSTAMP:20260506T010815
CREATED:20260210T120802Z
LAST-MODIFIED:20260325T123033Z
UID:12159-1775579400-1775583000@dimag.ibs.re.kr
SUMMARY:Mamadou Moustapha Kanté\, Strongly flip-flat classes of graphs
DESCRIPTION:Strong flip-flatness appears to be the analogue of uniform almost-wideness in the setting of dense classes of graphs. Almost-wideness is a notion that was central in different characterisations of nowhere dense classes of graphs\, and in particular the game-theoretic one. In this talk I will present the flip-flatness notions and conjectures about the characterization of strongly flip-flat graph classes. Then\, I will present a proof that strongly flip-flat classes of graphs that are weakly sparse are indeed uniformly almost-wide\, making a step towards their characterisation. A consequence is a characterization of strongly flip-flat graph classes with low rank-depth colourings. \nThis is a joint work with F. Ghasemi\, J. Grange and F. Madelaine.
URL:https://dimag.ibs.re.kr/event/2026-04-07/
LOCATION:Room B332\, IBS (기초과학연구원)
CATEGORIES:Discrete Math Seminar
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DTSTART;TZID=Asia/Seoul:20260428T163000
DTEND;TZID=Asia/Seoul:20260428T173000
DTSTAMP:20260506T010815
CREATED:20260303T004153Z
LAST-MODIFIED:20260303T004338Z
UID:12388-1777393800-1777397400@dimag.ibs.re.kr
SUMMARY:Xin Wei\, Separating hash families with large universe
DESCRIPTION:Separating hash families are useful combinatorial structures that generalize several well-studied objects in cryptography and coding theory. Let $p_t(N\, q)$ denote the maximum size of the universe for a $t$-perfect hash family of length $N$ over an alphabet of size $q$. We show that $q^{2 – o(1)} < p_t(t\, q) = o(q^2)$ for all  $t \ge 3$\, thereby resolving an open problem raised by Blackburn et al. (2008) for certain parameter ranges. Previously\, this result was known only for $t = 3$ and $t = 4$. Our approach establishes the existence of a large set of integers that avoids nontrivial solutions to a system of correlated linear equations. This is joint work with Xiande Zhang and Gennian Ge.
URL:https://dimag.ibs.re.kr/event/2026-04-28/
LOCATION:Room B332\, IBS (기초과학연구원)
CATEGORIES:Discrete Math Seminar
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