wtf is book3_elements-of-mathematics?

This repository contains the third book in a series called "Elements of Mathematics," which is part of a Chinese-language educational project nicknamed the Feather Book series. The book is described as covering a path from basic arithmetic all the way to machine learning, with topics including linear algebra, matrices, and data science concepts. The content is stored as Jupyter Notebooks, which are interactive documents that can combine written explanations, math formulas, and runnable code in the same file. This format is commonly used in data science and math education because it lets readers see both the theory and working examples side by side. The repository's README is written in Chinese and is quite brief. It provides links to discount purchase pages hosted on Zhihu, a Chinese knowledge-sharing platform, and notes that the open-source materials will remain available permanently. The authors also mention that readers who spot and report errors may receive a complimentary copy of the book as a thank-you. Based on the topics listed, the material covers mathematics subjects that are frequently used as foundations for machine learning, including linear algebra and matrix operations. The repository appears to be an open companion to a paid printed or digital book, with the Jupyter Notebooks serving as the interactive, freely accessible portion of the course.