Asserting reference inequality

Question

Is there a way for including assertions in a LaTeX document? I want to check that some condition is true, and only allow compilation of the document if it is (or at least complain otherwise).

Specifically, a paragraph contains a reference to a chapter. Before compiling the final version, I'd like to be warned if the chapter is the current chapter, so that I could e.g. substitute the text with "in this chapter".

Answer 1

Here is an idea that goes a bit beyond your question. You can do this with the ifthen package and by defining a new command. The command \mychapterref{#1} checks if the argument (a reference) is the current chapter. If it is, it writes out the string this chapter, otherwise it writes out Chapter~\ref{#1}.

\documentclass{report}
\usepackage{ifthen}

\begin{document}

\newcommand{\mychapterref}[1]{%
\ifthenelse{\equal{\ref{#1}}{\arabic{chapter}}}{this chapter}{Chapter~\ref{#1}}
}

\chapter{begin}\label{chap1}
look in \mychapterref{chap1}

\chapter{next}
look in \mychapterref{chap1}

\end{document}

The code above outputs

look in this chapter

in Chapter 1 and

look in Chapter 1

in other chapters.