序数，是指总能比较大小的东西，大小关系满足三歧性和传递性，而且任何序数组成的集合都存在最小值。序数分为0（最小的序数）、后继序数（比它小的序数之中有最大值）、极限序数（比它小的序数之中没有最大值）三种。

在所有由“顶点k染色的树”组成的，而且满足下面的两个条件的序列中，序列的最大长度就记作TREE (k)。 这里，顶点染色的树之间的嵌入关系比较复杂，但可以转换成下面这个比较简单的定义。 如果树A能够通过有限次“去掉一个叶子”和“去掉一个子顶点数为1的顶点，并把它的子顶点和它的父顶点连接起来”操作变成树B，那么B就能嵌入A。 定义到此为止。 由定义看出，tree (-1)无定义。 当然，你可以根据它的意义进行拓展，例如zeta函数就是拓展出来的。 这个问题没有定义 …

In mathematics, Kruskal's tree theorem states that the set of finite trees over a well-quasi-ordered set of labels is itself well-quasi-ordered under homeomorphic embedding. The theorem was conjectured by Andrew Vázsonyi and proved by Joseph Kruskal (1960); a short proof was given by Crispin Nash-Williams (1963).

3 天之前 · 生成树（spanning tree）：一个连通无向图的生成子图，同时要求是树。 也即在图的边集中选择 条，将所有顶点连通。 无根树的叶结点（leaf node） ：度数不超过 的结点。

2015年1月28日 · 树（Tree）：n（n≥0）个结点构成的有限集合。 当n=0时，称为“空树”；对于任一棵“非空树”（n>0），它具备以下性质： 其余结点可分为m（m≥0）个“互不相交”的有限集T 1， T 2，...， T m，其中每一个集合本身又是一棵树，称为原来树的“子树（SubTree）”。 特点： 一棵N个结点的树有N-1条边。 【一些基本术语】 路径和路径长度：从结点n 1 到n k 的 路径 为一个 结点序列n1，n2，...，nk。 n i 是n i+1 的父结点。 路径所包含 边的个数 为 路径的长度； 【二 …

In set theory, a tree is a partially ordered set (T, <) such that for each t ∈ T, the set {s ∈ T : s < t} is well-ordered by the relation <. Frequently trees are assumed to have only one root (i.e. minimal element), as the typical questions investigated in this field are easily reduced to questions about single-rooted trees.

A node’s depth is the distance (in number of nodes) from it to the root. The root itself has depth zero. In our example, B is of depth 1, E is of depth 3, and A is of depth 0. height (of a tree). A rooted tree’s height is the maximum depth of any of its nodes; i.e., the maximum distance from the root to any node. Our example has a height of ...

TREE(2) is 3. The first tree can only be the unique one-vertex tree, labelled with either 1 or 2, it doesn't matter which. Say we label it with 1. Then no remaining trees can use the label 1; all vertices must be labelled with 2. The second tree can either be the unique one-vertex tree or the unique two-vertex tree.

2018年1月14日 · Binary Tree: 00 | _____ | | 00 00 |__ | __ | | | | 00 00 00 00 对于二叉树的遍历，主要有以下三种基本遍历方式： 先序遍历 ：先显示节点值，再显示左子树和右子树

Ordered binary trees are a classic data structure to store and access data efficiently. Each node has only two branches, the left and the right one. Data is stored at each node (not only at leaf) and it is enforced that all the data below the left branch is smaller than the node value, and all the data on the right branch is bigger than the value.