> 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/2017/02/18.md).

# 18

![](https://385430918-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-M8iFCzaIpXf8zXqpE6I%2F-MTY47Kn_QwcFrK_tSAi%2F-MTY4R23O4LRI0nKL2tF%2Fimage.png?alt=media\&token=8f781a94-ee9c-449c-bd0c-bfcaf8b0bd44)