\documentclass[a4paper, 12pt]{article}

\usepackage{graphics}
\begin{document}


\section{Paragraphs and line spacing}

Testing of spacing. The next music is surrounded by an empty line.
text text text text text text text text text text text text
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{%
\parindent 0pt
\noindent
\ifx\preLilyPondExample \undefined
\else
  \expandafter\preLilyPondExample
\fi
\def\lilypondbook{}%
\input{67/lily-ff28cae4-systems.tex}
\ifx\postLilyPondExample \undefined
\else
  \expandafter\postLilyPondExample
\fi
}

text text text text text text text text text text text text
text text text text text text text text text text text text
text text text text text text text text text text text text

The next music has no surrounding empty lines.
text text text text text text text text text text text text
text text text text text text text text text text text text
text text text text text text text text text text text text
{%
\parindent 0pt
\noindent
\ifx\preLilyPondExample \undefined
\else
  \expandafter\preLilyPondExample
\fi
\def\lilypondbook{}%
\input{67/lily-ff28cae4-systems.tex}
\ifx\postLilyPondExample \undefined
\else
  \expandafter\postLilyPondExample
\fi
}
text text text text text text text text text text text text
text text text text text text text text text text text text

\end{document}