Possible Duplicate:

How to look up a symbol?

I'd like to write the unity element 1 in LaTeX. I have tried these methods:

```
$\mathbbm{1}$ \\
$\mathbb{1}$\\
$\mathbbss{1}$\\
$\mathbbtt{1}$\\
$\mathds{1}$\
```

but I receive the integer 1. I think that I'm missing a suitable package. How to solve this problem?

## Best Answer

The "standard" blackboard bold math font contains only uppercase latin-alphabet letters. To get a blackboard bold "1" symbol, you need to load an additional LaTeX package.

For instance, the commands

`\mathbb{1}`

(load the`bbold`

package) and`\mathds{1}`

(load the`dsfont`

package) will generate:respectively.