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Re: [Chicken-hackers] Re: Backdoor GPL in message-digest

From: John Cowan
Subject: Re: [Chicken-hackers] Re: Backdoor GPL in message-digest
Date: Tue, 24 Aug 2010 14:16:58 -0400

On Tue, Aug 24, 2010 at 1:29 PM, Peter Bex <address@hidden> wrote:

> That's not what I said.  I said you can't link a LGPL library to a GPL
> library.  You said you *can* link a GPL library to a LGPL library, which
> is of course correct (but the other way around).

Ah, I see: we are using the term "link to" in different senses.

You can release a library Foo under the LGPL even though it depends on
the library Bar which is under the GPL.  Any program using both Foo
and Bar must be released under the GPL, of course (and in fairness you
should warn me of that), but I could modify Foo under the terms of the
LGPL to create Foo2, with no dependency on Bar, and then use Foo2 in a
proprietary program.  If Foo had been under the GPL, I could not do

For this reason, the Pure interpreter
<>, which is mostly under the LGPL,
comes with two main programs: one under the GPL which depends
readline, and one under a BSD license which does not.  Consequently, I
could develop my own proprietary main program starting with the BSD
version.  But if the author had not provided the BSD version, I could
not myself remove the readline dependency in the GPL version and use
the rest of the code in a proprietary program.  (Although the GPL
version will link with editline if readline is not available, the
author has chosen not to try to take advantage of that gray area.)

> >From what I understand of it, writing an LGPL library on top of a GPL
> library is simply not allowed because that would require the "upper"
> library to be GPLed too.  The GPL library forces everything on top of
> it to be GPL.

If you released Foo+Bar as a combined library, that library as a whole
would have to be under the GPL, yes.  That does not mean that its
components must all be.

> For a practical example, there's MySQL. People have cursed MySQL not
> just for being a crappy database but also for the fact that their client
> libraries are (or used to be?) GPL.  I couldn't write a mysql Chicken
> Scheme egg which binds the MySQL client libraries and release the egg
> under LGPL, for instance.

That particular problem no longer exists, because Oracle now grants
additional permissions for the (GPL2-only) client libraries to be used
under the LGPL and other FOSS licenses.  See for details.

Note: When I say "must be released", I always mean "must be released if at all".

Same disclaimer as before.

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