> 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/2019/08/20.md).

# 20

<figure><img src="https://385430918-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2F-M8iFCzaIpXf8zXqpE6I%2Fuploads%2FH2sGLYBCsMvyiYCTjj7L%2Fimage.png?alt=media&amp;token=bc9e9a8f-4d5b-4d77-ad79-1fe2bfb71bfb" alt=""><figcaption></figcaption></figure>