port my notes from here https://gist.github.com/namoopsoo/fa903799b958ffc9f279cd293e83e9d9 and here https://gist.github.com/namoopsoo/df08c674b4e3e4794e97601682242c51

and here https://gist.github.com/namoopsoo/607f29e923ceaba890588e69293413cf