lilypondbook with multiple files

[Stefan Thomas]

Dear community,
I have problems processing a latex-file with lilypond-book and latex, which consists of more than one parts.
Here is my example:
%%%% the "master file" %%%%%%%%%%%

\documentclass[a4paper]{article}

\begin{document}
\input partone.tex
\input parttwo.tex
\end{document}

% the file partone.tex

This is an example with text and music! \\
\begin{lilypond}
 \version"2.12.2"
\relative {c4 d e f g a b c}
\end{lilypond} \\

% the file parttwo.tex

This is another example with text and music! \\
\begin{lilypond}
 \version"2.12.2"
\relative c'' {c4 b a g f e d c}
\end{lilypond} \\

I tried to process it with the following script:

#!/bin/zsh
mkdir -p out/
lilypond-book --pdf $1.tex --output=out
cd out/ &&
pdflatex "$1".tex
mv "$1".pdf ../
cd ../ &&
rm -r out/

When I do so, I get the message:

! I can't find file `partone.tex'.
l.6 \input partone.tex
Please type another input file name:

 I can't find my mistake.
I tried it also with the ending lytex instead of latex