《算法导论(第4版)》学习第 20 天，p91-p94 总结，总计 4 页。
一、技术总结
1. recursion tree
In graph theory, a recursive tree (i.e., unordered tree) is a labeled, rooted tree. A size-n recursive tree's vertices are labeled by distinct positive integers 1, 2, …, n, where the labels are strictly increasing starting at the root labeled 1.
二、英语总结(生词：1)
1. ground
(1)ground
vt. to establish the base(foundation) of something/base something on something(为......建立基础，奠定......的基础),
(2)示例
You ground the induction on a range of values from a convenient positive constant n₀ up to some constant n₀′ > n₀ such that for n ≤ n₀ the recurrence always bottoms out in a constant-sized base case between n₀ and n₀′(《《算法导论(第4版)》》第 91 页)。
关于英语的注解同步更新汇总到 https://github.com/codists/English-In-CS-Books 仓库。
三、其它
这样太慢了，不得行，得加快进度。
四、参考资料
1. 编程
(1) Thomas H. Cormen，Charles E. Leiserson，Ronald L. Rivest，Clifford Stein，https://book.douban.com/subject/35591269/
2. 英语
(1) Etymology Dictionary：https://www.etymonline.com
(2) Cambridge Dictionary：https://dictionary.cambridge.org
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