# Blackboard bold characters

The blackboard bold font in the AMSFonts package only has capital letters. I sometimes wish to use a blackboard bold "1", for which I can use \usepackage{bbold}. But this changes the entire blackboard bold font, and I like the original AMSFonts versions of the capital letters better. Is there a simple way for me to get \mathbb{1} from one package and and the blackboard bold capitals from another?

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This doesn't exactly answer your question (how to use bbold with AMS's black board bold characters). I believe that would require some TeX incantations.

A cheaper work around is to use either the package bbm or the package doublestroke. The former defines the \mathbbm command and the latter uses the \mathds command, so they don't conflict with the AMS \mathbb. Also asthetically I prefer the bbm fonts over bbold since the latter is sans serif, which doesn't quite fit in right against the AMS serifed fonts.

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That may not answer the question precisely as I asked it, but it tells me how to do what I want to do. The sans serif issue is also my aesthetic complaint with the bbold font. –  Mark Meckes Jul 28 '10 at 16:58
@MarkMeckes: Note that \mathbbm selects a Type 3 font whereas \mathds selects a Type 1 font. –  mhp Sep 3 '11 at 21:08

I had the same question about a year ago. I came up with the following solution, which seems a bit cleaner that Juan's "hack":

\DeclareSymbolFont{bbold}{U}{bbold}{m}{n}
\DeclareSymbolFontAlphabet{\mathbbold}{bbold}


Then one can use $\mathbbold{1}$ (and I store this, without the dollar signs, in the macro \ind since I use it as an indicator function).

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You've already got a pretty good answer. Just in case you really wanted to use amsmath and bbold, the following TeX-hack seems to do the trick.

\usepackage{amsmath}
\usepackage{amsfonts}
\makeatletter
\def\amsbb{\use@mathgroup \M@U \symAMSb}
\makeatother

\usepackage{bbold}

\begin{document}
$\mathbb{1}, \amsbb{X}$
\end{document}

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Well, I don't really want to do that, but I may well find myself wanting to use a similar hack for a different purpose sometime. –  Mark Meckes Jul 28 '10 at 18:00
Here is another way to do what you want that leaves \mathbb using the AMS fonts.
\newcommand{\bbfamily}{\fontencoding{U}\fontfamily{bbold}\selectfont}

You can then use \mathbbold for the bbold math fonts.
Welcome to TeX.SX! A tip: You can use backticks ` to mark your inline code as I did in my edit. –  Adam Liter Jan 23 at 20:25