科研之友
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摘要
Let T-k be a family of all k-vertex trees. For T subset of T-k, and a tree T, we write T -%26gt; T if T contains at least one of the trees from 7 as a subtree, we write T 74 7 otherwise. Let ex(T) be the smallest integer n, if such exists, such that for any tree T on at least n vertices T -%26gt; T. It is shown that min{ex(7) : T subset of T-k, vertical bar T vertical bar=q} =2 Theta(k log(q-1) k), where log(q-1) is the q - 1 times iterated logarithm. In addition, the bounds on ex(7) for families 7 with a given number of spiders are given.
- 出版日期2013-4-28
