# Do I need a specific package for “\N”

The wikepedia page Folge has this formula (under Formale Definition)

\begin{matrix} a:&\N &\to &X\\ & i &\mapsto &a_i, \end{matrix}

where \N is used for the set of natural numbers. I am able to create its symbol with a \mathbb{N}. But when I use \N, I get the error ! Undefined control sequence..

I assume I need to use a specific package in order to have \N defined. Is this so and if so, which one is it?

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no just define \N yourself: \usepackage{amsfonts} \newcommand\N{\mathbb{N}} – David Carlisle Dec 21 '12 at 12:53
I see. Does wikipedia do this definition "behind the scenes"? – René Nyffenegger Dec 21 '12 at 12:57
Instead of that font I use dsfonts package, which defines \mathds{} instead of \mathbb{} and gives you better output (in my opinion). – Manuel Dec 21 '12 at 14:38