X headers

Hi all.

First thanks, as usual, for all the great work in bringing free music
software to the world.

I installed DeMudi from the "demudi_1.2.0-rc2_i386.iso" CD and ran
"upgrade-demudi" as detailed in the "Package Updates" section of this web
page:

  http://demudi.alioth.debian.org/wiki/DocumentsFAQ

with

  deb http://apt.agnula.org/demudi/ testing main local extra
  deb http://snapshot.debian.net/archive/2004/07/14/debian/ testing main
contrib non-free

in "/etc/apt/sources.list".

I then tried building a project from source code and discovered that there
were no X headers installed (eg Xlib.h, X.h etc, confirmed with "find
/ -iname Xlib.h").  So I did:

  apt-get install libx11-6

and the system claimed it was already installed.

So I did:

  apt-get --reinstall install libx11-6   # From memory here

This downloaded and reinstalled the package, but still no X headers.  So my
question is:

  Which package should I be using to get "Xlib.h" and friends on Demudi?

Cheers

Mike Thomas.