1. Who can use this document freely?

If you are a teacher or a student belonging to an educational organization, you can freely use this document and figures in your study. Anyone can use this document and figures with noncommercial meetings and lectures, if you state the link to this site and the copyright; otherwise, contact me.

2. Does the author need any help to write?

No. I am writing for my own enjoyment. Even if you send me your article, I will never include it in my document.

3. Why doesn't the author use the GitBook or other e-book formats/sites?

I am using the best tools I need and I will decide what I use. I am always trying a lot of tools for better explanations. For instance, I modified the google-code-prettify and used JavaScript and MathJax, etc.
Simply put, this docment is optimized to read on html file and it is hard to convert to other formats.

4. Why doesn't the author use RSS to notify the update?

I keep my domain and my server to provide my document; you can read when you want to read. What do you want more?

5. Why doesn't the author waive the copyright of this document or use the creative commons license?

I'd like to ask you what problems you have by that I keep on having the copyright of my document.