[Tex/LaTex] Using versions environment tags inside a new environment definition

conditionalsenvironments

I just found out about the versions package here and am interested in using it to hide solutions in a problem set document. Recall that, to create versions block, in the preamble, you need

\usepackage{versions}  
\excludeversion{sol}  
%\includeversion{sol}

and, in the document,

\begin{sol} ... \end{sol}

Here, the blocks labeled "sol" will be excluded.

In my document, I define a new environment "Solution" as 

\newenvironment{Solution}{\begin{sol} \\ \textbf{Solution: }}{\end{sol}}

This construction works perfectly if I instruct LaTeX to include the "sol" blocks, but chokes if I try to exclude them. For example, the following code chokes and gives an Incomplete \iffalse error:

\documentclass{article}  
\usepackage{versions}  
\excludeversion{sol}  
%\includeversion{sol}  
\newenvironment{Solution}{  
  \begin{sol}\\ \textbf{Solution: }}{  
  \end{sol}}  
\begin{document}  
\section{Question 1}  
What is $2+2$?  
\begin{Solution}  
It is $2+2=4$.  
\end{Solution}  
\end{document}

If I change the commenting and include "sol", then this code works as expected. I'm guessing that there's something going on with the way that the versions package works. Any suggestions?

Best Answer

Don't use \begin{sol} ... \end{sol} in the definition of the Solution environment. \begin ... \end blocks don't nest very well. Rather, use \sol ... \endsol. Thus:

\documentclass{article}
\usepackage{versions}
\excludeversion{sol}
%\includeversion{sol}
\newenvironment{Solution}{
\sol\\ \textbf{Solution: }}{
\endsol}
\begin{document}
\section{Question 1}
What is $2+2$?
\begin{Solution}
It is $2+2=4$.
\end{Solution}
\end{document}

works.

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