I have the following expression

```
$$\left\{\varphi\in\text{End}\left({\widetilde{E}/\overline{\F}_{\Pf}}\right)\mid \varphi\text{Frob}_{\Pf}=\text{Frob}_{\Pf}\varphi\right\}$$
```

and would like to know how to match the length of `\mid`

to the length of `\left\{`

and `\right\}`

. Thanks!

## Best Answer

For middle stretchable delimiters you can use

`\middle`

:Notice also the use of

`\DeclareMathOperator`

to produce the right font and spacing for "End" and "Frob". Also,`$$...$$`

shouldn't be used in modern LaTeX documents; use`\[...\]`

instead. Since I didn't know the definitions of some commands, I defined them provisionally.