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Re: Bug#251885: ITP: cgal -- C++ library for computational geometry

Joachim Reichel wrote:
> License:
> The library consists of three modules. The lower layers (Kernel and the
> Support library) are licensed under LGPL, the upper layer (Basic Library) is
> licensed under QPL. Code under LGPL and code under QPL is combined in one
> library.
> I've CC'ed debian-legal and I would like to know whether both licenses are
> compatible.

If the two licenses only applied to different libraries that linked to
each other, they would be compatible, because the scope of the LGPL
deliberately stops at the library boundary.  However, the LGPL requires
that all code which directly incorporates LGPLed code be LGPLed.
>From the LGPL, version 2.1:
>   The precise terms and conditions for copying, distribution and
> modification follow.  Pay close attention to the difference between a
> "work based on the library" and a "work that uses the library".  The
> former contains code derived from the library, whereas the latter must
> be combined with the library in order to run.
>   The "Library", below, refers to any such software library or work
> which has been distributed under these terms.  A "work based on the
> Library" means either the Library or any derivative work under
> copyright law: that is to say, a work containing the Library or a
> portion of it, either verbatim or with modifications and/or translated
> straightforwardly into another language.  (Hereinafter, translation is
> included without limitation in the term "modification".)
>   2. You may modify your copy or copies of the Library or any portion
> of it, thus forming a work based on the Library, and copy and
> distribute such modifications or work under the terms of Section 1
> above, provided that you also meet all of these conditions:
>     a) The modified work must itself be a software library.
>     b) You must cause the files modified to carry prominent notices
>     stating that you changed the files and the date of any change.
>     c) You must cause the whole of the work to be licensed at no
>     charge to all third parties under the terms of this License.

So any "work based on the library" must be licensed under the LGPL.
Since the QPL is not compatible with the LGPL, the entire work is

The other issue here is that the QPL is not a Free Software license at
all.  See the thread starting at
<http://lists.debian.org/debian-legal/2004/04/msg00233.html> for
details.  The QPL requires that all changes are sent to the original
author upon request, and that all license disputes are settled in
Amsterdam City Court by the laws of the Netherlands.  Both of these
restrictions are non-DFSG-free.

I would suggest asking the authors to dual-license their library under
the QPL and the GPL, like Trolltech did with Qt.  In addition to solving
the freeness and compatibility problems, this would also makes the
library GPL-compatible, which allows the huge number of GPLed programs
to link with the library.

(Incidentally, the libcwd package which raised the issue of the QPL
seems to have been uploaded to main even after that discussion concluded
that the license was non-free.)

- Josh Triplett

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