I'm new in this mailing-list, i'm french and i don't speak english very well, so I started badly :-)
I use
Lilypond for some time now, and I often find my answers in the
documentation (very well done), the LSR and on the French mailing-list, very
active! But this time, no one has figured out how to achieve what I want. As pictures speak louder than words, I send you what I'd like to achieve.
A bass line that splits into two with braces and returns on a single line.