The structure of the problem and the kind explanations of the two teachers are both so good. I want to recommend it to people around me. However, there is a lecture with an error in the explanation. (No. 69, 70) Someone else has already asked about it on the Q&A board, and the teacher kindly corrected it in the answer. However, I think it needs improvement for students like me who solve it on their own and only check the video explanation. I wonder if I should keep clicking Q&A every time I watch the video lecture, and I am a little worried that there may have been another error that I did not know about before. It would be good if you could give me a hint that there is an error, like you posted the revised explanation for No. 54. Thank you for the great lecture. -------------------------------------------------------------- As soon as I posted the review above, you immediately organized the errors and shared them in the notice. I was touched by the quick feedback, so I revised it to 5 stars,,,