Re: License info request

[Alfred M. Szmidt]

   I am in the process of putting together a source code package for a
   library we use.  The source code consists of a number of different
   modules which are all labelled in one of the following ways:

   1. Code written by me which I have labelled as being under the GPL.

Ok.

   2. Code written by Alice and modified by me which is labelled by
   Alice as being under the GPL.

Should also be labled that it has been modified by you.

   3. Code written by Bob and modified by me which is labelled by Bob as
   being Public Domain.

Ok.

   4. Code written by Carol and modified by me which is labelled as
   "Licence is also granted to make and use derivative works provided
   that such works are identified as 'derived works from the RSA Data
   Security (Oops, I mean Carol!), Inc BARF-Jiggle Algorithm' in all
   material mentioning or referencing the derived work."

Ok.

   I guess my question is am I in some way 'diluting' the GPL status
   of my own code and mods to other GPLd code by including PD and
   'free but proprietary' code in my library package?

You cannot include proprietary licensed code into a GPL licensed
project.  If you include Public Domain material, then the license for
the whole work will still be the GPL (see section 2(b) of GPLv2, I do
not have a copy of GPLv3 to quote it right now)

How is the license in point 4 non-free by the way?

   I _think_ that in case 3, I can put a GPL notice on the code,
   stating that my modified version of this code is henceforth subject
   to the GPL, and that the original code was in the public domain and
   can obtained from Bob's web-wite.

Since it was PD, you can even remove any mention of Bob.

   Oh, and if there's an FAQ about GPL issues such as this, I'd
   appreciate a pointer in the right direction.

There is, http://www.gnu.org/licenses/gpl-faq.html

Cheers.