Render mathematical formulas using KaTeX.
Set `math: true` in `book.json`:
```json
{
}
```
Use `$...$` for inline formulas:
```markdown
The equation $E = mc^2$ is famous.
```
Use `$$...$$` for display (block) formulas:
```markdown
$$
\int_0^\infty e^{-x^2} dx = \frac{\sqrt{\pi}}{2}
$$
```
For supported functions and syntax, see the [KaTeX documentation](https://katex.org/docs/supported).