Cleanup

[seewoo5]

• Remove unused imports
• Lint
• max3 to avoid max (max a b) c

[jcpaik]

Progress of #10

• [x] Remove unused imports
• [x] Lint
• [x] max3 to avoid max (max a b) c
• [x] use .nat_degree to avoid noisy and unfriendly with_bot nat

[seewoo5]

Also this is really minor opinion, but I prefer sort imports with alphabetical order (in python we have a package called isort)