% A comment on the first line should not confuse lilypond-book's format
% detection
\documentclass[a4paper, 12pt]{article}

\begin{document}

\section{A comment on the first line of the file}

The source file for this document contains a comment on the first line.
This should not confuse the auto-detection of lilypond-book...

\begin{lilypond}
\score{
  \relative c'{c d e f g a b c}
}
\end{lilypond}

\end{document}