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
A subfamily of sets is a non-induced (weak) copy of a poset P in if there exists a bijection such that implies . In the case where in addition holds if and only if , then is an induced (strong) copy of P in . We consider the minimum number [resp. ] of sets that a family 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 creates a non-induced [induced] copy of P.
We prove for any finite poset P that , 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 for some constant depending only on P or . We classify several posets according to this dichotomy, and also show better upper and lower bounds on and 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 集合是一个非诱导(弱)一个偏序集的副本P在 如果存在双射 以至于 暗示 . 在另外的情况下 成立当且仅当 , 然后 是诱导的(强)的副本P在. 我们考虑最小数量 [分别。 ] 套那一个家庭 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,添加任何创建P的非诱导 [诱导] 副本。
我们证明了任何有限偏序集P是,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要么对于一些仅取决于P或的常数. 我们根据这种二分法对几个偏序集进行分类,并在 和 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。