GPL: what does redistribution mean?

["Marcelo E. Magallon" <mmagallo@efis.ucr.ac.cr>]

Hi,

	I've been meaning to ask this for quite a while, but I haven't found
the time to sit down and actually write something.

As part of my research, I'm writing a program that I think will be useful to
other people in the astronomical/astrophysical community.  I want to license
this program under the GPL, but I still have to sort some details out,
namely, I need to find out if I'm allowed to license this under the GPL,
taking into account that I've been using a great deal of resources from my
University.  The other detail is something that's been bugging me and is the
reason for this email...

Up to a certain degree, I'm sure some people will have interest in extending
and modifying the program for their own research.  Let's say some research
group finds my codebase useful, and extend it into a direction I haven't had
the time to work on, or just didn't occured to me was possible.  If this is
done by one person, in the privacy of their own computer, that's ok, they
don't have to publish the modifications.

If this person publishes a paper based on my work and his modifications,
that's ok, too, he doesn't have to publish the modifications.

But what if this person gives copy of the modified sources (or binaries) to
a colleague... in the same research group?  Is that "internal use"?  Does
that qualify as redistribution?  I think it does, I just want a
confirmation.  Even further, if the group (Foo Bar et al) publishes a paper
for which the modified program was used, can I demand the changes to be
published, based on the fact I would have evidence (because of the "et al")
the program was redistributed? (I admit it wouldn't be hard evidence)

I'm just trying to make this program free software, and prevent the usual
abuse that I've seen on the "scientific community" at the same time...
(everyone is willing to publish papers, but almost noone is willing to
publish source code -- and some papers are worthless without access to the
programs used to perform the simulations, but yet they are published)


	Marcelo