I remember when I first entered middle school and encountered the unknown number x. When I got to know it, x, which at best had the meaning of a question mark, made me feel vaguely afraid. No one told me that it was just a blank space, and as time went by, x hid itself deep in the middle of a formula. I still couldn't shake off that fear, so I took gg as a 5th grade math test... .. Learning is like building a castle. It can be a sand castle or an impregnable fortress. This lecture is like digging into the x above. It explains things that seem difficult in a simple and clear way. Therefore, I dare to say that there is no lecture better than this one to lay an impregnable foundation for those who want to study related fields. The lecture has a rhythm. It's hard to explain, but it feels like a rhythm of heavy and heavy mori. The time signature is 4/4, and the lecture progresses in a funky flow, so if you follow this flow, you can listen to the end without getting bored and with interest. (Honestly, excluding regular expressions.) In my opinion, a really good lecture is one where you come up with an idea that applies what you learned while listening to the lecture, and you feel confident that you can actually do it. This lecture is really like that. It is a lecture that gives hope without showing off. —Lecture critic Kim Moon-gwa-soon—