Dual licensing with two copyleft licenses

[Evan Prodromou]

On Thu, 2004-02-12 at 06:20 -0800, Brian Behlendorf wrote:
> On Thu, 2 Dec 2004, Evan Prodromou wrote:
> > My understanding, then, is that Bob must choose one or the other license
> > offered by Alice. Since both of these licenses require derivative works
> > to be licensed identically, Bob's derivative work must have the same
> > license as the one he chose to use.
> 
> Can't Bob make that decision twice?  Release two packages, one under 
> license A, one under license B, both of them the same package of the 
> original work plus his modifications and thus, the same work?

Well, that's a good question. As I see it, that depends on the wording
of the copyleft license. Some examples:

     1. GNU GPL: "You must cause any work that you distribute or
        publish, that in whole or in part contains or is derived from
        the Program or any part thereof, to be licensed as a whole at no
        charge to all third parties under the terms of this License."
        This seems open to allowing other licenses, although I'm not
        clear on the mechanics.
     2. GFDL: "You may copy and distribute a Modified Version of the
        Document under the conditions of sections 2 and 3 above,
        provided that you release the Modified Version under precisely
        this License, [...]". "Precisely this license" says to me that
        the modified version can't be dual-licensed.
     3. Creative Commons ShareAlike: "You may distribute, publicly
        display, publicly perform, or publicly digitally perform a
        Derivative Work only under the terms of this License,". "Only",
        here, seems to preclude dual-licensing to me, too.
     4. OSL: "to distribute copies of the Original Work and Derivative
        Works to the public, with the proviso that copies of Original
        Work or Derivative Works that You distribute shall be licensed
        under the Open Software License;". Later sections mentioning "or
        another written agreement between Licensor and You" seem to be
        designed specifically to allow dual-licensing.
     5. MPL: Designed to allow derived works to be licensed under the
        same two licenses as the original work.

So, I think the answer is: kinda.

~ESP

-- 
Evan Prodromou                  .O.
http://bad.dynu.ca/~evan/       ..O
evan at bad.dynu.ca                OOO
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