# How can you change \mathbb characters to the old version?

If you look at older documents the \mathbb characters appear different. For example they are sans serif. I don't know how I can use that set of characters instead of the current default.

If you are not sure what version I am talking about load the package fourier and then use \mathbb{C} for example to see the difference. No other package beside fourier does that and I want to know how to do it with other packages.

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Your question is not very clear, but let's see if I can understand it. What you want is to obtain the \mathbb font from the fourier package but without changing the rest of the fonts? –  Juan A. Navarro Aug 16 '10 at 9:06
You can't use them yet without seriously modifying your LaTeX documents and workflow, but the blackboard bold character in the STIX font also look similar to fourier. –  Caramdir Aug 16 '10 at 9:26
Btw, for those that do not want to try it: This is what the fourier \mathbb font looks like: caramdir.at/uploads/tex.SE/fourier-mathbb.png –  Caramdir Aug 16 '10 at 9:29
@ Juan. Yes and if you look at older Math publication what is in fourier now used to be the standard some 20 years ago. –  Hesam Aug 16 '10 at 9:29
@hesam: when i started using tex, the fonts msxm and msym were in use; they were only available in archaic metafont (which wouldn't compile by the mid-80s when i started), and some (iirc) pxl files at a low resolution. the ams paid for a new version to be written, and there was outcry back then about the lost serifs (i forget what barbara beeton -- then as now, the public face of the ams in the tex world -- said about the complaints). anyway, i think yours is the first complaint i've seen, about this, for something like 20 years! –  wasteofspace Mar 9 '12 at 9:45

The following is a hack that seems to do the work, it actually comes from the source of the fourier package.

\documentclass{article}

\DeclareFontFamily{U}{futm}{}
\DeclareFontShape{U}{futm}{m}{n}{
<-> s * [.92] fourier-bb
}{}
\DeclareSymbolFont{Ufutm}{U}{futm}{m}{n}
\DeclareSymbolFontAlphabet{\mathbb}{Ufutm}

\begin{document}
Hello World $\mathbb{C}$
\end{document}

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This does work. I was hoping there would be a more clean solution like you load some package or activate some option of the \mathbb{} command. But thank you. –  Hesam Aug 16 '10 at 9:30
Yo could try the solutions proposed by others (which seem easier) to check if they work for you. Otherwise you can throw this code in a .sty file and include it using \usepackage. In any case, if you like this answer please feel free tu up-vote/accept it :) –  Juan A. Navarro Aug 16 '10 at 9:41
In particular, bbold, mathbbol and mbboard provide sans-serif fonts. The last two also provide additional symbols in blackboard bold.