Stephen Turner <[EMAIL PROTECTED]> writes: > But I am getting a bit confused here. Take the zlib licence, for example, > which contains the condition: > 3. This notice may not be removed or altered from any source distribution. > The FSF says that this is compatible with the GPL, but I don't understand > how this can be so. It imposes an extra restriction, namely the requirement > to reproduce the zlib copyright and licence notice, in addition to the terms > of the GPL. Can someone explain to me how this can be GPL-compatible?
Section 2 of the GPL says that modified versions of a GPL'd work must be distributed "under the terms of this License". The GPL itself, in section 1, requires that you publish with an "appropriate copyright notice". The requirement of, say, the X Consortium license, that you preserve its copyright notice is itself part of an "appropriate copyright notice"; the GPL itself mandates that you keep it around. It is sometimes thought that the GPL prohibits "adding additional conditions", but that's just a shorthand. What it actually requires is that modified versions be distributed "under the terms of this License", which is not *quite* the same thing.