# GitBook FAQ

#### Should I use an `.html` or `.md` extensions in my links?

You should always use `.md` extensions for your relative links, GitBook will automatically replace these links by the right value when the pointing file is referenced in the Table of Contents.

#### Can I create a GitBook in a sub-directory of my repository?

Yes, GitBooks can be created in [sub-directories](structure.md#subdirectory). GitBook.com and the CLI also looks by default in a serie of [folders](structure.md).

#### Does GitBook support Math equations?

GitBook supports math equations and TeX thanks to plugins. There are currently 2 official plugins to display math: [mathjax](https://plugins.gitbook.com/plugin/mathjax) and [katex](https://plugins.gitbook.com/plugin/katex).