> For the complete documentation index, see [llms.txt](https://www.oulan.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://www.oulan.com/2017/03/20.md).

# 20

![](https://385430918-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-M8iFCzaIpXf8zXqpE6I%2F-MTY-d1ETnEtt3jpCD7T%2F-MTY-khvzRFXllZrJrh0%2Fimage.png?alt=media\&token=d4e77822-f706-449e-8720-614b78e8dc1f)