> 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/2017/03/21.md).

# 21

![](https://385430918-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-M8iFCzaIpXf8zXqpE6I%2F-MTY-o0c-sKwS4tTrJc0%2F-MTY-xjmx_l5Zwxl9rRm%2Fimage.png?alt=media\&token=b23e0b43-f4a1-4d54-9493-f39ec400eefd)