> 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/2016/12/21.md).

# 21

![](https://385430918-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-M8iFCzaIpXf8zXqpE6I%2F-MHQAdR7HHzAenMGpgvn%2F-MHQBG5ecuD6C98_TZev%2Fimage.png?alt=media\&token=57469458-1785-432b-bec4-0f66f003d84e)