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Possible Duplicate:
Blackboard bold characters

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


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?

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

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

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:






The resulting output is:

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