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Induced and non-induced poset saturation problems
Journal of Combinatorial Theory Series A ( IF 1.1 ) Pub Date : 2021-07-02 , DOI: 10.1016/j.jcta.2021.105497
Balázs Keszegh 1, 2 , Nathan Lemons 3 , Ryan R. Martin 4 , Dömötör Pálvölgyi 2 , Balázs Patkós 1, 5
Affiliation  

A subfamily GF2[n] of sets is a non-induced (weak) copy of a poset P in F if there exists a bijection i:PG such that pPq implies i(p)i(q). In the case where in addition pPq holds if and only if i(p)i(q), then G is an induced (strong) copy of P in F. We consider the minimum number sat(n,P) [resp. sat(n,P)] of sets that a family F2[n] can have without containing a non-induced [induced] copy of P and being maximal with respect to this property, i.e., the addition of any G2[n]F creates a non-induced [induced] copy of P.

We prove for any finite poset P that sat(n,P)2|P|2, a bound independent of the size n of the ground set. For induced copies of P, there is a dichotomy: for any poset P either sat(n,P)KP for some constant depending only on P or sat(n,P)log2n. We classify several posets according to this dichotomy, and also show better upper and lower bounds on sat(n,P) and sat(n,P) for specific classes of posets.

Our main new tool is a special ordering of the sets based on the colexicographic order. It turns out that if P is given, processing the sets in this order and adding the sets greedily into our family whenever this does not ruin non-induced [induced] P-freeness, we tend to get a small size non-induced [induced] P-saturating family.



中文翻译:

诱导和非诱导偏集饱和问题

一个亚科 GF2[n]集合是一个非诱导(弱)一个偏序集的副本PF 如果存在双射 一世G 以至于 q 暗示 一世()一世(q). 在另外的情况下q 成立当且仅当 一世()一世(q), 然后 G是诱导的(强)的副本PF. 我们考虑最小数量(n,) [分别。 (n,)] 套那一个家庭 F2[n]可以在不包含P的非诱导 [诱导] 副本的情况下具有并且对于该属性是最大的,即,添加任何G2[n]F创建P的非诱导 [诱导] 副本。

我们证明了任何有限偏序集P(n,)2||-2,一个与地面集的大小n无关的边界。对于诱导副本P,有一个二分法:对任何偏序集P要么(n,)对于一些仅取决于P或的常数(n,)日志2n. 我们根据这种二分法对几个偏序集进行分类,并在(n,)(n,) 对于特定类别的poset。

我们的主要新工具是基于字典顺序对集合进行特殊排序。事实证明,如果给定P,按此顺序处理集合并贪婪地将集合添加到我们的家庭中,只要这不会破坏非诱导 [诱导] P自由度,我们往往会得到一个小尺寸的非诱导 [诱导] ] P-饱和族。

更新日期:2021-07-04
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