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Re: ELPA license, LGPL + additional restrictions

On Fri, 2 Nov 2012 16:13:10 +0100 Michael Banck wrote:

> (Please CC me on replies, as I am not subscribed currently).


> The development version (not in testing/unstable for now) of cp2k, which
> is under the GPLv2+ itself has just added support for the ELPA library:
> they say ELPA is licensed
> under the LGPL with some additional clauses.
> It says this:
> --8<--
> The code is distributed under ALMOST all of the the terms of the GNU
> Lesser General Public License version 3 (LGPL).
> While we are not allowed to alter the license texts as written in those 
> files, IN ADDITION our own license prescribes two important
> modifications / clarifications to the original lgpl.txt:
> - In point 2., clause b) - stating that that you may redistribute
>   under the terms of the plain GNU GPL - shall NOT apply. In other
>   words, if you redistribute, you MUST keep the additional permissions
>   of the LGPL v3 in place.
> - If you redistribute, you must redistribute under the terms of the
>   LGPL version specified here. Using later or earlier versions
>   published by anyone except the ELPA copyright holders is
>   not allowed. 
> --8<--
> My main question would be whether the above can considered
> GPLv2+-compatible, i.e. whether cp2k can use this.

Dear Michael,
first of all the GNU LGPL v3 is not compatible with the GNU GPL v2, but
only with the GNU GPL v3.
Hence, even a plainly LGPLv3-licensed work would be considered
compatible with a GPLv2+-licensed work, just because of that plus sign
(assuming that "v2+" means "v2 or later", as usual), but not with a
GPLv2only-licensed work.

However, this case is much more complicated, since there are two
additional clauses, with respect to the GNU LGPL v3.

The first clause disables one clause of the GNU LGPL v3, dropping its
one-way convertibility to the ordinary GPL.
My own personal opinion is that such additional restriction (which I am
not even sure can actually be added this way to the GNU LGPL v3) makes
the result GPL-incompatible.
The reason is that the GNU GPL insists that the whole work be available
under the terms of the GNU GPL, but the above restriction makes this
impossible for the ELPA library.

The second clause seems actually unnecessary to me: as specified by
Section 6 of the GNU LGPL v3, a library is not compelled to enable the
"or later" mechanism:

| If the
| Library as you received it specifies that a certain numbered version
| of the GNU Lesser General Public License "or any later version"
| applies to it, you have the option of following the terms and
| conditions either of that published version or of any later version
| published by the Free Software Foundation.

It says "*If* the Library [...] specifies [...]", so the Library may
specify otherwise (for instance "v3 only").
The LGPL text even allow the licensor to elect a "proxy" that will
decide whether future versions shall apply...
Hence, I personally think that there's no need to add this second
clause to achieve this result.
I am under the impression that it should suffice to specify "v3 only",
which is already the case:

| The code is distributed under ALMOST all of the the terms of the GNU
| Lesser General Public License version 3 (LGPL).

or perhaps to specify that the ELPA Consortium is the proxy that will
decide whether future versions shall apply.

> The other question would be how to best approach the ELPA folks to
> make them feel alright that the LGPLv3+ is fine for them.

This is more tricky.
Persuasion is a difficult art and I don't feel particularly clever at
it in these times...   :-(

I hope my reply helps a bit.

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..................................................... Francesco Poli .
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