# \choose

Plain-TeX infix binomial-style form with parentheses as fixed delimiters and no fraction bar.

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

## Metadata

| Field | Value |
| --- | --- |
| Topic | [Fractions and roots](https://texform.dev/latex/topics/fractions-roots) |
| Packages | base |
| Allowed mode | math |
| Tags | discouraged |
| Commonality | medium |
| Kind | infix |

## Syntax

### base

Argument specification: ``

Plain-TeX infix binomial-style form with parentheses as fixed delimiters and no fraction bar.

## Examples

```latex
a \choose b
```

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

## Renderer support

| Package | MathJax | KaTeX | XeTeX |
| --- | --- | --- | --- |
| base | full | full | full |

## Usage frequency

0.21% of formulas in the measured corpus contain this entry, rank 85 of 263 entries with frequency data.

## In TeXForm

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

### Discouraged in base

This is a plain-TeX infix generalized fraction primitive. LaTeX documents typically prefer \binom or \genfrac because they use explicit braced arguments.

```latex
$1 \choose $2 -> \binom{$1}{$2}
```

\binom is the standard LaTeX command for binomial-style fractions, uses explicit braced arguments, and avoids the ambiguous scope of the infix primitive.

```latex
$1 \choose $2 -> \genfrac{(}{)}{0pt}{}{$1}{$2}
```

\genfrac exposes the generalized-fraction parameters explicitly and avoids infix-scope ambiguity.

### [base/choose-to-binom](https://texform.dev/rules/base/choose-to-binom)

Rewrite infix choose to an explicit binom command.

Level: authoring. Fidelity: render.

```latex
#1 \choose #2
```

→

```latex
\binom{#1}{#2}
```

```latex
n+r-1 \choose 2k+1
```

→

```latex
\binom{n+r-1}{2k+1}
```

## Equivalent forms

```latex
\binom{$1}{$2}
```

exact. 

```latex
\genfrac{(}{)}{0pt}{}{$1}{$2}
```

exact. 

## See also

- [\\above](https://texform.dev/latex/commands/above)
- [\\abovewithdelims](https://texform.dev/latex/commands/abovewithdelims)
- [\\atop](https://texform.dev/latex/commands/atop)
- [\\atopwithdelims](https://texform.dev/latex/commands/atopwithdelims)
- [\\brace](https://texform.dev/latex/commands/brace)
- [\\brack](https://texform.dev/latex/commands/brack)
- [\\over](https://texform.dev/latex/commands/over)
- [\\overwithdelims](https://texform.dev/latex/commands/overwithdelims)

## Test cases

### base

| Input | Case | MathJax | KaTeX | XeTeX |
| --- | --- | --- | --- | --- |
| a \choose b | Positive: baseline | Pass | Pass | Pass |