As the name of this blog, “知之为知之，不知为不知 (To know what you know and what you do not know, that is true knowledge. — by Confucius)”, this blog is basically a place for me to save the Q&A from Internet during my research and life. The majority of the posts are directly from the Internet, with the source links given. If you are the author of certain post, and not happy with my re-post, please let me know, and I will delete it.
Overall, I would like to share the knowledge I learned from the Internet; hopefully, it will also be useful for you.