Journal of Combinatorial Theory Series A ( IF 0.9 ) Pub Date : 2020-02-13 , DOI: 10.1016/j.jcta.2020.105228 Chong Shangguan , Itzhak Tamo
For fixed integers , let be the maximum number of edges in an r-uniform hypergraph in which the union of any e distinct edges contains at least vertices. A classical result of Brown, Erdős and Sós in 1973 showed that . The degenerate Turán density is defined to be the limit (if it exists) Extending a recent result of Glock for the special case of , we show that for arbitrary fixed . For the more general cases , we manage to show where the gap between the upper and lower bounds are small for .
The main difficulties in proving these results are the constructions establishing the lower bounds. The first construction is recursive and purely combinatorial, and is based on a (carefully designed) approximate induced decomposition of the complete graph, whereas the second construction is algebraic, and is proved by a newly defined matrix property which we call strongly 3-perfect hashing.
中文翻译:
稀疏超图的简并图兰密度
对于固定整数 ,让 是r均匀超图中的最大边数,其中任何e个不同边的并集至少包含顶点。布朗,埃尔德斯和索斯在1973年的经典结果表明:。退化的图兰密度定义为极限(如果存在) 扩展了Glock的最新结果,用于特殊情况下 ,我们证明 对于任意固定 。对于更一般的情况,我们设法证明 上下限之间的间隙较小 。
证明这些结果的主要困难是确定下界的构造。第一个结构是递归的和纯的组合,并且基于(精心设计)近似引起的完全图的分解,而第二结构是代数,由我们称之为新定义的矩阵属性证明强烈3 -完美散列。