Possible Duplicate:
Blackboard bold characters

I have seen the unit (or identity operator) typeset via

\newcommand{\unit}{1\!\!1}

Is this really the best way to get a double-stroke 1? The obvious guess, \mathbb{1}, does not work.

Or is the use of a double-stroke 1 (rather than "Id" or just a simple "1") for this purpose frowned upon?

marked as duplicate by Joseph Wright Sep 3 '11 at 20:44

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  • I would highly recommend \usepackage{bbm} and \newcommand\idop{\bbm 1}. – Niel de Beaudrap Sep 3 '11 at 20:53
  • This can be confusing. – Wok Dec 4 '12 at 12:38

Try \mathds from the dsfont package:

\documentclass{article}

\usepackage{dsfont}

\begin{document}

\noindent
\(\mathds{1}\)

\end{document}

The resulting output is:

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