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Re: Licensing a work using a GPL-ed library under the LGPL

Shriramana Sharma <samjnaa@gmail.com> writes:

> http://www.fsf.org/licensing/licenses/gpl-faq.html#AllCompatibility
> says that a work using a GPL-ed library can be licensed under the
> LGPL "if you convert to GPL". For example the KDE libraries which
> use the GPL-ed Qt libraries are themselves licensed under the LGPL.

Not quite; I believe it's the other way around. To release the
combined work, the only license compatible with both GPLv2 and LGPLv2.1 is

This is only true because the LGPLv2.1 contains this test as §3:

      3. You may opt to apply the terms of the ordinary GNU General Public
    License instead of this License to a given copy of the Library.  To do
    this, you must alter all the notices that refer to this License, so
    that they refer to the ordinary GNU General Public License, version 2,
    instead of to this License. [...]
      Once this change is made in a given copy, it is irreversible for
    that copy, so the ordinary GNU General Public License applies to all
    subsequent copies and derivative works made from that copy.

The GPLv2 contains no such "conversion" clause, so may only be
combined with works licensed under the GPL. Thus, the only way an LGPL
work can be thus combined and redistributed is to "convert" the work
to the GPL license and release the combined work under the GPL.

> But I don't understand what is the meaning of licensing something
> under the LGPL if it is effectively under the GPL anyway because it
> uses a GPL-ed library.

Because it also allows linking with works that are *not* under LGPL.

> So what is the point in licensing it under the LGPL?

If you want to allow the library to be linked with non-free software.

> Could it be that parts of such a work which do not use a GPL-ed
> library can be used under the LGPL? Is there such a legal
> distinction between "parts that use the GPL-ed library" and "parts
> that don't"?

I don't really understand this question. I hope the above makes it

> A related question is about the people who have contributed code to
> Qt under BSD/MIT-style licenses [...]
> In that case, how can their code which uses GPL-ed Qt be licensed
> under anything other than the GPL?

The BSD and MIT-style licenses allow redistribution under any license
terms, so redistributing such works under GPL terms is compatible with
all three licenses.

 \       "Pinky, are you pondering what I'm pondering?" "Well, I think |
  `\    so, Brain, but I can't memorize a whole opera in Yiddish."  -- |
_o__)                                            _Pinky and The Brain_ |
Ben Finney

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