https://nju-sicp.bitbucket.io/2021/projs/proj02/index.html
HINT
https://www.bilibili.com/video/BV1s3411G7yM?vd_source=d21f89893c9e3093d77e243b2e781f93&spm_id_from=333.788.videopod.episodes&p=2
