How to

[François Bastien]

Hello,

I make some tweaks to the default layout, and I would want to
conditionally  add an `arr.` before the arranger name on one of my custom
layout. This is used to produce two music sheets, one compact and one
large, the large containing the `arr. Somebody`, and the compact containing
`Somebody`

I tried this:
```
\version "2.24.1"
\header {
  arranger = "" % or arranger = "Somebody"
}

%something

#(define (should-not-print-arranger layout props) (eq? "" 'header:arranger))

% something else

% in the large.ly file:
\unless \should-not-print-arranger
           \smaller \italic \line {
            "arr."
            \fromproperty  #'header:arranger
          }
```
but this dont work.

It works if I use `should-print-all-headers` in the `\unless` block.

I have a thousand browser tabs open on different parts of the lilypond /
guile documentation and source code, but I can't find what is my error, any
help would be greatly appreciated.

Thanks
-- 
François Bastien