Font selection problem

Question

I need a blackboard bold 1. I know the font bbold provides it along with 0, but if I declare the math alphabet via:

\DeclareSymbolFond{bbold}{U}{bbold}{m}{n}
\DeclareMathAlphabet{\bbold}{bbold}

or the likes, I get a too many math alphabets used error message which I cannot resolve because my very complex package mixes many fonts and produces the error, and the combination I want is the one in force and I don't want to engage in a messy editing of the package which is absolutely huge. I found a workaround here which brought me to:

\documentclass[a4paper]{report}
\usepackage{amsmath,amssymb,amsfonts}
\begin{document}
[\mathbb{Z}\quad{\fontencoding{U}\fontfamily{bbold}\fontseries{m}\fontshape{n}\selectfont 1\csname U/bbold/m/n\endcsname1}.]
\fontencoding{U}\fontfamily{bbold}\fontseries{m}\fontshape{n}\selectfont1
\end{document}

This outputs:

I notice the font selection commands work only in text mode. Now I could, of course, switch to text mode every time I need a blackboard bold 1, which is not very often, but I don't like the idea too much. So I was wondering: why do the 1s in math mode stay in their normal font? Why is there no warning of any kind about this font substitution? And how do I make these commands work in math mode, or anyway select that font in math mode (without the commands at the question's top of course)?

Answer 1

The set up for fonts is split into a configuration for text and a configuration for maths. Settings for one do not affect settings for the other. So, every time you switch to maths mode, you activate a different set of fonts. Of course, if you use \text{} or something, you switch temporarily back to text. But, while in maths mode, you are using the maths fonts. For (pdf)TeX, the 16 font allowance is a hard limit. I don't think there is much you can do. However, you could define a wrapper to switch to text and the blackboard font seamlessly within maths mode.

For example, you could do something like this which does switch to text mode, but doesn't require spelling out the switch each time:

\documentclass[a4paper]{report}
\usepackage{amsmath,amssymb,amsfonts}
\DeclareRobustCommand{\mybbold}{%
        \fontencoding{U}%
        \fontseries{m}%
        \fontshape{n}%
        \fontfamily{bbold}%
        \selectfont}
\DeclareTextFontCommand{\textbb}{\mybbold}
\begin{document}
\[
\mathbb{Z}\quad{\fontencoding{U}\fontfamily{bbold}\fontseries{m}\fontshape{n}\selectfont 1\csname U/bbold/m/n\endcsname1}.
\]
\fontencoding{U}\fontfamily{bbold}\fontseries{m}\fontshape{n}\selectfont Z 1
\[
\textbb{Z 1}
\]
\end{document}