problem with footer

[Jose-Luc Hopital]

Lilypond version 2.4.2 on windoze XP or 2.4.1 on linux

I like to put a non-amiguous but readable small text on every page
of music , for example "Corelli Sonata op1-1 V1" for the Violin 1 part.
The \footer variable seem to be useful for that , but nothing is visible
in the PDF output. I have tried to put a "footer = " in a header block
(or paper or layout ) inside a book or a score block without success.

The documentation say 
The header and footer are created by the functions make-footer 
and make-header, defined in \paper. The default implementations 
are in scm/page-layout.scm.

I don't understand...

In a word, how to obtain a footer ?
Thanks.