# \underset

Places one math expression beneath a base expression, commonly for labels or annotations under operators, relations, or arrows.

https://texform.dev/latex/commands/underset

## Metadata

| Field | Value |
| --- | --- |
| Topic | [Accents](https://texform.dev/latex/topics/accents) |
| Packages | base |
| Allowed mode | math |
| Tags |  |
| Commonality | medium |
| Kind | prefix |

## Syntax

### base

Argument specification: `m m`

Places one math expression beneath a base expression, commonly for labels or annotations under operators, relations, or arrows.

## Common tasks

### How to put a label under a relation

```latex
A \underset{\mathrm{open}}{\subset} B
```

[Open in Playground](https://play.texform.dev/?input=A+%5Cunderset%7B%5Cmathrm%7Bopen%7D%7D%7B%5Csubset%7D+B)

### How to write an arrow with a condition below

```latex
x_n \underset{n\to\infty}{\longrightarrow} x
```

[Open in Playground](https://play.texform.dev/?input=x_n+%5Cunderset%7Bn%5Cto%5Cinfty%7D%7B%5Clongrightarrow%7D+x)

### How to annotate an equality from below

```latex
a \underset{(1)}{=} b
```

[Open in Playground](https://play.texform.dev/?input=a+%5Cunderset%7B%281%29%7D%7B%3D%7D+b)

## Examples

```latex
\underset ab
```

[Open in Playground](https://play.texform.dev/?input=%5Cunderset+ab)

```latex
\underset{x+y}{z}
```

[Open in Playground](https://play.texform.dev/?input=%5Cunderset%7Bx%2By%7D%7Bz%7D)

## Renderer support

| Package | MathJax | KaTeX | XeTeX |
| --- | --- | --- | --- |
| base | full | full | none |

## Usage frequency

0.50% of formulas in the measured corpus contain this entry, rank 65 of 263 entries with frequency data.

## In TeXForm

TeXForm parses this entry as prefix syntax; the package determines its argument specification.

## Test cases

### base

| Input | Case | MathJax | KaTeX | XeTeX |
| --- | --- | --- | --- | --- |
| \underset{a}{b} | Positive: baseline | Pass | Pass | Fail |
| \underset a{b} | Positive: bare[0] | Pass | Pass | Fail |
| \underset{a}b | Positive: bare[1] | Pass | Pass | Fail |