# \|

The ‖ symbol (Double vertical line, U+2016), written as \| in LaTeX math mode.

https://texform.dev/latex/symbols/-7c-

## Metadata

| Field | Value |
| --- | --- |
| Topic | [Delimiters](https://texform.dev/latex/topics/delimiters) |
| Packages | base |
| Allowed mode | math |
| Glyph | ‖ |
| Unicode | U+2016 DOUBLE VERTICAL LINE |
| Delimiter |  |

## Syntax

```latex
\|
```

Takes no arguments.

## Common tasks

### How to write a double vertical bar / norm

The symbol page for | is the control sequence \| (‖), not the bare | character.

```latex
\|x\|
```

[Open in Playground](https://play.texform.dev/?input=%5C%7Cx%5C%7C)

### How to write a stretchy norm

```latex
\left\| \frac{a}{b} \right\|
```

[Open in Playground](https://play.texform.dev/?input=%5Cleft%5C%7C+%5Cfrac%7Ba%7D%7Bb%7D+%5Cright%5C%7C)

### How to write an operator norm

```latex
\|A\|_{\mathrm{op}}
```

[Open in Playground](https://play.texform.dev/?input=%5C%7CA%5C%7C_%7B%5Cmathrm%7Bop%7D%7D)

## Usage frequency

4.60% of formulas in the measured corpus contain this entry, rank 22 of 474 entries with frequency data.

## In TeXForm

TeXForm parses this entry as a character leaf mapped to U+2016 (DOUBLE VERTICAL LINE).

## See also

- [\\|](https://texform.dev/latex/commands/-7c-)