Junsang Chi! First of all, thank you for leaving a review. You have taken 35% of the course, but it seems that my lecture did not suit you well. If you had written specifically which part was lacking, I would have provided you with a supplement. I am sorry and regretful..! I apologize again for not being able to provide a satisfactory lecture. I will come back with a satisfactory lecture next time. Thank you again for your valuable feedback.