# Defining LaTeX Macros
**URL:** https://talk.observablehq.com/t/defining-latex-macros/1310
**Category:** Help
**Created:** [October 11, 2018, 3:12pm UTC](https://talk.observablehq.com/t/defining-latex-macros/1310 "2018-10-11T15:12:21Z")
**Posts on this page:** 2
**Page:** 1
### Author:  [@krisrs1128](https://talk.observablehq.com/u/krisrs1128)
#### Post date: [October 11, 2018, 3:12pm UTC](https://talk.observablehq.com/t/defining-latex-macros/1310/1 "2018-10-11T15:12:21Z")
Is it possible to define LaTeX macros in a notebook? For example, I would like to write `${tex`\def\reals{\mathbb{R}`}` somewhere and then be able to refer to `${tex`\reals`}` elsewhere (ideally, across different blocks).
---
### Author:  [@mbostock](https://talk.observablehq.com/u/mbostock)
#### Post date: [October 11, 2018, 3:48pm UTC](https://talk.observablehq.com/t/defining-latex-macros/1310/2 "2018-10-11T15:48:30Z")
There are a few ways to do this, but the best option may be to augment the standard library slightly to allow passing options through to KaTeX.
We’re using [KaTeX 0.10-beta](https://github.com/Khan/KaTeX/releases), which _does_ support `\def`, but this only affects the given input to `tex`—it doesn’t persistently change the behavior of `tex`. This is good because it avoids mutable state and nondeterministic behavior. (KaTeX also appears to support `\gdef`, which sounds like it would persistently change the behavior of `tex`, but I couldn’t get it to work and wouldn’t recommend it anyway.)
Defining a macro to use it once isn’t especially useful, but it works:
```auto
tex`\def\reals{\mathbb{R}} \reals^2`
```
To make reusable macros, you could have a _macros_ cell to define your macros, and then embed them wherever you call `tex`. Note you’ll need String.raw to avoid double-backslashes.
```auto
macros = String.raw`\def\reals{\mathbb{R}}`
```
```auto
tex`${macros}\reals^2`
```
You can go one step further and define a wrapper for `tex` that has your macros in it:
```auto
function mtex() {
return tex`
\def\reals{\mathbb{R}}
${String.raw.apply(String, arguments)}
`;
}
```
```auto
mtex`\reals`
```
If you want total control, here’s how do define your own template literal using KaTeX directly:
```auto
katex = require("katex")
```
```auto
function mtex() {
const root = document.createElement("div");
katex.render(String.raw.apply(String, arguments), root, {
macros: {
"\\reals": "\\mathbb{R}"
}
});
return root.removeChild(root.firstChild);
}
```
In the future, I’d like something like this:
```auto
mtex = tex.options({
macros: {
"\\reals": "\\mathbb{R}"
}
})
```