The following lines caught my attention while browsing `source2e`

while looking for the definition of another command.

```
\DeclareMathRadical{\sqrtsign}{symbols}{"70}{largesymbols}{"70}
```

and

```
\DeclareRobustCommand\sqrt{\@ifnextchar[\@sqrt\sqrtsign}
\def\@sqrt[#1]{\root #1\of}
```

What was `\sqrtsign`

for? I tried `\sqrtsign{x}`

and it outputs something similar to `\sqrt{x}`

.

## Best Answer

The definition of LaTeX's

`\sqrt`

iswhich means that if the optional argument is used (i.e., if the next character after

`\sqrt`

is`[`

),`\@sqrt`

is used (and this in its turn, uses`\root#1\of`

whose definition can be found on page 210 of`source2e.pdf`

) to typeset the radical index and the subradical expression; if no optional argument is given,`\sqrtsign`

is used to typeset the subradical expression (`\sqrtsign`

doesn't allow an optional argument).