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arXiv 1808.01065math.COmath.PR
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大围长近似Steiner三元系

Large girth approximate Steiner triple systems

Tom Bohman, Lutz Warnke

摘要:

在1973年鄂尔多斯问是否有n-顶点部分施泰纳三元系与任意高围长和二次许多三元组。(Here围长被定义为最小整数g \ge 4,对于该最小整数g 4,某些g元顶点集至少包含g-2个三元组。通过证明任意高围长的近似Steiner三元系的存在性,我们回答了这个问题。更具体地说,对于任何固定的\ell \ge 4,我们表明,一个自然的约束随机过程通常会产生一个部分Steiner三元系,具有(1/6-o(1))n^2个三元组,围长大于\ell。该过程在围长保持大于\ell的约束下迭代地添加随机三元组。我们的结果是最好的可能的o(1)-项,这是一个负的n的幂。

英文摘要:

In 1973 Erdos asked whether there are n-vertex partial Steiner triple systems with arbitrary high girth and quadratically many triples. (Here girth is defined as the smallest integer g \ge 4 for which some g-element vertex-set contains at least g-2 triples.) We answer this question, by showing existence of approximate Steiner triple systems with arbitrary high girth. More concretely, for any fixed \ell \ge 4 we show that a natural constrained random process typically produces a partial Steiner triple system with (1/6-o(1))n^2 triples and girth larger than \ell. The process iteratively adds random triples subject to the constraint that the girth remains larger than \ell. Our result is best possible up to the o(1)-term, which is a negative power of n.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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