\documentclass{article}

\input{include/def.tex}

\usepackage{graphics}
\begin{document}

If the include file in the preamble is not available,
the automatic line width detection would fail and the
snippet below would have only one bar per line.

{%
\parindent 0pt
\noindent
\ifx\preLilyPondExample \undefined
\else
  \expandafter\preLilyPondExample
\fi
\def\lilypondbook{}%
\input{91/lily-2b21d285-systems.tex}
\ifx\postLilyPondExample \undefined
\else
  \expandafter\postLilyPondExample
\fi
}

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\end{document}