Restore original definition of $

Question

I found an incompatibility between onlyamsmath and tabu, related to the redefinition of the $-sign. (Its is an active char, and thus breaks inside tabu columns specifiers). This is triggered with:

\documentclass{article}
\usepackage{amsmath}
\usepackage[all,error]{onlyamsmath}
\usepackage{tabu}
\begin{document}
\begin{tabu} to 0.6\textwidth{X[c]X[c]X[$c]} 
a & b & c\\ 
\end{tabu} 
\end{document}

If I could restore the original definition of $ at the beginning of the document I could work around the bug. Note that I want to include this 'bugfix' in a package and can not rely on the correct loading order. So I do not want to enforce loading before onlyamsmath.

Answer 1

You can patch the tabu environment so that it sets the correct catcode

\usepackage{tabu}
\usepackage{etoolbox}
\AtBeginEnvironment{tabu}{\catcode`$=3 }

In this way the "protection" given by onlyamsmath is disabled only inside the tabu environment.

Answer 2

You need to set the catcode of $ back to its normal value of 3. However, onlyamsmath does this at-begin-document and you need to change it back after that. In order to ensure that, you can use the filehook package and then:

\AtEndOfPackageFile*{onlyamsmath}{\AtBeginDocument{\catcode`\$=3\relax}}

Which will install the required code in the at-begin-document hook at the end of onlyamsmath, if it gets loaded or immediately, if it was already loaded.

Full example (both orders work):

\documentclass{article}
\usepackage{amsmath}

\usepackage{filehook}
\AtEndOfPackageFile*{onlyamsmath}{\AtBeginDocument{\catcode`\$=3\relax}}

\usepackage[all,error]{onlyamsmath}
\usepackage{tabu}

%\usepackage{filehook}
%\AtEndOfPackageFile*{onlyamsmath}{\AtBeginDocument{\catcode`\$=3\relax}}

\begin{document}
\begin{tabu} to 0.6\textwidth{X[c]X[c]X[$c]} 
a & b & c\\ 
\end{tabu} 
\end{document}