arXiv subjects

Gyula O. H. Katona

Publications and source records attributed to Gyula O. H. Katona.

24 records · Page 2Linked to original sources

arXiv2017

A general 2-part Erd\H os-Ko-Rado theorem

A two-part extension of the famous Erdős-Ko-Rado Theorem is proved. The underlying set is partitioned into $X_1$ and $X_2$. Some positive integers $k_i, \ell_i (1\leq i\leq m)$ are given. We prove that if ${\cal F}$ is an intersecting family containing members $F$ such that $|F\cap X_1|=k_i, |F\cap X_2|=\ell_i$ holds for one of the values $i (1\leq i\leq m)$ then $|{\cal F}|$ cannot exceed the size of the largest subfamily containing one element.

math.CO↗

arXiv2016

Around the Complete Intersection Theorem

The celebrated theorem of Ahlswede and Khachatrian determines the maximum size of a family of $k$-element subsets of an $n$-element set where the intersection of any two subsets has at least $r$ elements. This survey first gives a historical introduction, then it shows some applications.

math.CO↗

arXiv2014

Union-intersecting set systems

Three intersection theorems are proved. First, we determine the size of the largest set system, where the system of the pairwise unions is l-intersecting. Then we investigate set systems where the union of any s sets intersect the union of any t sets. The maximal size of such a set system is determined exactly if s+t<5, and asymptotically if s+t>4. Finally, we exactly determine the maximal size of a k-uniform set system that has the above described (s,t)-union-intersecting property, for large enough n.

math.CO↗

arXiv2013

Incomparable copies of a poset in the Boolean lattice

Let $B_n$ be the poset generated by the subsets of $[n]$ with the inclusion as relation and let $P$ be a finite poset. We want to embed $P$ into $B_n$ as many times as possible such that the subsets in different copies are incomparable. The maximum number of such embeddings is asymptotically determined for all finite posets $P$ as $\frac{n \choose \lfloor n/2\rfloor}{M(P)}$, where $M(P)$ denotes the minimal size of the convex hull of a copy of $P$. We discuss both weak and strong (induced) embeddings.

math.CO↗

arXiv2012

Majority and Plurality Problems

Given a set of n balls each colored with a color, a ball is said to be majority, k-majority, plurality if its color class has size larger than half of the number of balls, has size at least k, has size larger than any other color class; respectively. We address the problem of finding the minimum number of queries (a comparison of a pair of balls if they have the same color or not) that is needed to decide whether a majority, k-majority or plurality ball exists and if so then show one such ball. We consider both adaptive and non-adaptive strategies and in certain cases, we also address weighted versions of the problems.

math.CO↗

arXiv2004

Largest family without A union B contained in C intersect D

Let F be a family of subsets of an n-element set not containing four distinct members such that A union B is contained in C intersect D. It is proved that the maximum size of F under this condition is equal to the sum of the two largest binomial coefficients of order n. The maximum families are also characterized. A LYM-type inequality for such families is given, too.

math.CO↗