Accessing public defines in scheme modules

[Simon Mackenzie]

If I use the following to load a scheme module into a lilypond script file I 
can use any of the public interfaces in this current file.
 
#(load "init/credits.scm")
#(use-modules (init credits)) %get access to the public defines in credits.scm

#(ech 'set-song-number "66.") % ech is a public define in credits.scm. happy to 
comply

but...
 if I have the following in the same or a dependant include file the public 
defines from credits.scm are now out of scope.

\book {
        \bookpart {
>>>             #(ech 'set-song-number "66.") % fails with a compilation error. 
>>> <<<
        }
}

How do I access the public define in the above scope? denoted by >>> <<<
I would assume I missed a straightforward way to accomplish this task.

Thank you
S Mack