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Some greedyt-intersecting families of finite sequences
Authors:Shiquan WU
Affiliation:(1) Department of Mathematics, National University of Technology, 410073 Changsha, China
Abstract:Letn, s1,s2, ... andsn be positive integers. Assume
$$mathcal{M}(s_1 ,s_2 , cdots ,s_n ) = { (x_1 ,x_2 , cdots x_n )|0 leqslant x_i  leqslant s_i ,x_i$$
is an integer for eachi}. For
$$a = (a_1 ,a_2 , cdots a_n ) in mathcal{M}(s_1 ,s_2 , cdots ,s_n )$$
,
$$mathcal{F} subseteq mathcal{M}(s_1 ,s_2 , cdots ,s_n )$$
, and
$$A subseteq { 1,2, cdots ,n}$$
, denotesp(a)={j|1lejlen,ajgep},
$$S_p (mathcal{F}) = { s_p (a)|a in mathcal{F}}$$
, and
$$W_p (A) = p^{n - |A|} prodlimits_{i in A} {(s_i  - p)}$$
.
$$mathcal{F}$$
is called anItp-intersecting family if, for any a,bisin
$$mathcal{F}$$
,aiLambdabi=min(ai,bi)gep for at leastt i's.
$$mathcal{F}$$
is called a greedyItP-intersecting family if
$$mathcal{F}$$
is anItp-intersecting family andWp(A)geWp (B+Ac) for anyAepsiSp(
$$mathcal{F}$$
) and any
$$B subseteq A$$
with |B|=t–1.In this paper, we obtain a sharp upper bound of |
$$mathcal{F}$$
| for greedyItp-intersecting families in
$$mathcal{M}(s_1 ,s_2 , cdots ,s_n )$$
for the case 2plesi (1leilen) ands1>s2>...>sn.This project is partially supported by the National Natural Science Foundation of China (No.19401008) and by Postdoctoral Science Foundation of China.
Keywords:Itp-greedy subsets  Itp-regular subset  t-intersecting family  Ipt-intersecting family  greedyItp-intersecting family
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