LGPL 2.1 + GPL 3 = problems?

[Philippe Verdy]

Note: the situation is exactly similar with the case where you want to
combine several works licenced with different versions of the GPL:
==> You can distribute your new combined work only under the terms of the
highest version of the individual licences of the GPL-covered components,
provided that they are ALL licenced with a copyright notice that explicitly
states that they allow this new higher version.

For this reason, it is highly recommended, for any programs you want to
publish under the GPL to use the terms "version x or any later version as
published by the Free Software Foundation" within your licencing terms.

If your copyright notice that references the appropriate licence to use only
specifies a precise version of the licence, you can still use a higher
version according to the terms of this referenced original licence. However,
if you really want to exclude any higher version, your copyright notice
should explicitly contain an "additional restriction" (as defined and
allowed in the GPL licences), such as:

	<one line for the name of the program and describing what it does>
	Copyright (C) <year> <author name>
	This library is a free software; you may redistribute it or modify
it
	according to the terms of the "GNU Lesser General Public License"
	version 2.1 as published by the Free Software Foundation, with the
	additional restriction that any later versions are excluded.

Without this EXPLICIT additional restriction in your copyright notice, the
original terms of the GPL v2.1 license allows upgrading the version of the
referenced license. Almost all GPL- or LGPL-licensed works do not have such
explicit "additional restriction", and can then be used or conveyed under
the terms of a newer version.

Reread for example the section 4 of the GPLv3 which explicitly states that
authors can decide which version of the GPL they accept. The "or any later
version" is an explicit statement that is now highly recommended, but this
is not the only option. GPLv3 allows later versions to be acceptable only
through acceptation by a given proxy. And it also allows an author to
enumerate the accepted version numbers.

These are viewed as additional permissions or restrictions, according to
section 7, which also allows changing the terms for the limitation of
warranty, or allows requiring or prohibiting the preservation of the
original author names, or limiting the usage of their personal names within
commercial products:

For example in trademarks where an author like "Linus Torvald" could
restrict the use of his name within the trademark of a commercial
distribution of a Linux Kernel, thus saying that the licence does not cover
the right to use this name in a trademark like "Torvald Linux (tm)" or in
ads like "Buy the unbreakable XYZ Linux now, featuring the new kernel
version x.y made by Linux Torvald" (in the countries where it would be legal
without permission unless the name was reserved, i.e. not in France at least
where French authors are also protected by their exclusive moral right
recognized by the Civil Law, so that French authors do not need to make such
explicit statement about the usage of their name, or photo, as this
exclusive protection by the French law on Authors Rights, now part of the
"DADVSI" Act, is extended internationally by WIPO in its binding treaties or
conventions).

Philippe