I am trying to incorporate some Unicode characters into my LaTeX files. All characters I added so far worked well, but when I use

```
\DeclareUnicodeCharacter{211D}{{\mathbb R}}
```

(211D is the Unicode character ℝ, i.e. what would be denoted `\mathbb{R}`

in LaTeX), I get an error message

```
Undefined control sequence ℝ
```

The problem is dependent neither on what is "…" in `\DeclareUnicodeCharacter{211D}{…}`

, nor on whether the character ℝ is used in math mode or not. For most other Unicode characters (even those with higher numbers), `\DeclareUnicodeCharacter`

works as expected, but I get the same error also for other double stroke letters (e.g. ℂ). Do you have any idea why this is so and how to make it work?

## Best Answer

The following works for me:

You probably forgot to load

amssymb. By the way, there's a different way to define such symbols without looking in Unicode tables:Notice also that the correct syntax is

`\mathbb{R}`

rather than`{\mathbb R}`

.