ThomaeAndNormal

\documentclass{book}
\usepackage{tikz}

\makeatletter
\pgfmathdeclarefunction*{gcd}{2}{%
	\begingroup
	\pgfmathcontinuelooptrue
	\pgfmath@xa=#1pt\relax % <-
	\pgfmath@xb=#2pt\relax % <-
	\ifdim\pgfmath@xa=0pt\relax
	\pgfmathcontinueloopfalse
	\pgfmath@xa=\pgfmath@xb
	\fi
	\ifdim\pgfmath@xb=0pt\relax
	\pgfmathcontinueloopfalse
	\pgfmath@xb=\pgfmath@xa
	\fi
	\ifdim\pgfmath@xa<0pt\relax
	\pgfmath@xa=-\pgfmath@xa
	\fi
	\ifdim\pgfmath@xb<0pt\relax
	\pgfmath@xb=-\pgfmath@xb
	\fi
	\loop
	\ifpgfmathcontinueloop
	\ifdim\pgfmath@xa=\pgfmath@xb
	\pgfmathcontinueloopfalse
	\else
	\ifdim\pgfmath@xa>\pgfmath@xb
	\advance\pgfmath@xa by-\pgfmath@xb\relax
	\else
	\advance\pgfmath@xb by-\pgfmath@xa\relax
	\fi
	\fi
	\repeat
	\pgfmathparse{int(\pgfmath@xa)}%
	\pgfmath@smuggleone\pgfmathresult
	\endgroup}
\makeatother

\includeonly{chapterNormal,chapterThomae} % LOOK HERE!!!!!!!!!!!!!!!!
\begin{document}
\include{chapterNormal} % A normal chapter with some tikz images
\include{chapterThomae} % The chapter with Thomae's function
\include{chapterLight} % A chapter with no images
\end{document}