Hello Gianmaria, I cannot talk about the other stuff, but the line
music = \new Voice \fixed c \ja s[ \jb s] % Valentin solution
Should be
music = \new Voice \fixed c { <<\ja s[>> <<\jb s]>> } % Valentin solution
Cheers,
Valentin
signature.asc
Description: This is a digitally signed message part.
