1-/ download the package and unzip it in a working directory (~/work for example).
2-/ go to ~/work/lilypond-doc_2.18.0-1_all/DEBIAN directory and suppress the files named "postinst", "postrm" and "preinst".
3-/ go to the extraction directory (~/work)
4-/ create the new deb file : dpkg -b lilypond-doc_2.18.0-1_all/ lilypond-doc_2.18.0-2_all.deb (I've changed the name of the file.deb but I'm not sure it is necessary).
5-/ install the new package with sudo dpkg -i lilypond-doc_2.18.0-2_all.deb.
Hi I think I found a way to solve the bug.
1-/ download the package and unzip it in a working directory (~/work for example). lilypond- doc_2.18. 0-1_all/ DEBIAN directory and suppress the files named "postinst", "postrm" and "preinst". doc_2.18. 0-1_all/ lilypond- doc_2.18. 0-2_all. deb (I've changed the name of the file.deb but I'm not sure it is necessary). doc_2.18. 0-2_all. deb.
2-/ go to ~/work/
3-/ go to the extraction directory (~/work)
4-/ create the new deb file : dpkg -b lilypond-
5-/ install the new package with sudo dpkg -i lilypond-
The doc is in place in the directory.