URLs in rbtree.c are broken

From the file header comment:

* rbtree.c
* implementation for PostgreSQL generic Red-Black binary tree package
* Adopted from http://algolist.manual.ru/ds/rbtree.php
*
* This code comes from Thomas Niemann's "Sorting and Searching Algorithms:
* a Cookbook".
*
* See http://www.cs.auckland.ac.nz/software/AlgAnim/niemann/s_man.htm for
* license terms: "Source code, when part of a software project, may be used
* freely without reference to the author."

The both URLs are no longer accessible.

For the first one, by search for “Thomas Niemann’s Sorting and Searching Algorithms: a Cookbook”, I got https://www.epaperpress.com/sortsearch/rbt.html, but I am not sure it provides the exactly same content as the old URL.

For the second one, I cannot find a replacement.

Best regards,
--
Chao Li (Evan)
HighGo Software Co., Ltd.
https://www.highgo.com/