I believe William explained it nicely, but just to make it clear: YOU wrote the program, so you have the rights to relicense it anyway you want even after you release it as GPL.
The point of GPL is to release the software to the public so that it can be used in a non-closed manner, but even when it's on the "wild" it still has your name all over it and nothing will prevent you from using your own code in a closed manner. However, you must be aware that any changes to a GPL program done by other people will remain GPL as by the terms of the license. That way, the "owner" of those patches are no longer you, so you can't relicense those patches as if it were part of the original (and as such you can't sell it). In other words, when you release the software, you can release it in any way you want, being it GPL or a dual-license, but those patches are not your own, so you become subject to the GPL too. Please keep in mind that this doesn't devalue your project, since it stays the same. If that's what you want it's for you to decide, but you can take a look at Trolltech's Qt (see http://en.wikipedia.org/wiki/Qt_(toolkit) ), which is a pretty visible example of double licensing: they have a GPL version which may be used by other GPL programs, but also have a commercial license for developers which want to build their own commercial programs. You can see many examples of that in the Wikipedia page above, but one program that stands out is Mathematica, which uses Qt itself but isn't GPL. Cheers, Ronan Paixão Electric Department Instituto Militar de Engenharia Em Sex, 2008-10-31 às 08:41 -0700, William Stein escreveu: > On Fri, Oct 31, 2008 at 8:35 AM, alunw <[EMAIL PROTECTED]> wrote: > > > > Thanks for this. > > > > I'll certainly consider doing this, though I'm still slightly > > concerned about the implications for my own code. I guess using the > > GPL is probably as good a way as any of deterring potential commercial > > competitors from "stealing" my code - though I'm not really expecting > > or even wanting to get rich it anyway. > > > > I'll post a suitable version on my web site in a day or two, and > > donate that. I hope it proves useful. > > > > Wonderful! I greatly appreciate this. And keep in mind that > it is your code that you own the copyright on, so if at any point > you want to use a less restrictive license, or sell the code > available for commercial use, that is still your right. > > So definitely include a statement in the README.txt that anybody > who is interested in using it under a different license than > GPL (e.g., BSD or something commercial) should definitely > contact you. This sort of thing does happen... > > Note: One issue you may have to (hopefully) "deal with" is that if somebody > might port your code to Linux/OS X/64-bit, etc., or fixes bugs, > they might only want their fixes to be available under the GPL > license, in which case you couldn't include them with a non-GPL'd > commercial version, at least without getting permission from that > person. > > Cheers, > William --~--~---------~--~----~------------~-------~--~----~ To post to this group, send email to [email protected] To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/sage-devel URLs: http://www.sagemath.org -~----------~----~----~----~------~----~------~--~---
