Subject: Re: Compatibility of the AFL with the GPL
From: Richard Stallman <rms@gnu.org>
Date: Sun, 16 Mar 2003 02:46:52 -0500

    The point of the law school exam being for anyone to be able to show a
    difference in people's behavior in re GPLed code versus AFL+GPLed
    code.  How can the licenses be said to be incompatible if the supposed
    incompatibility causes no change in anyone's behavior?

The presence of the AFL mutual defense clause would make a real
difference to people's behavior in the following case.

Suppose W is under the GPL and X is under the AFL.  P combines them
and distributes X+W to Q saying it is licensed under the GPL.  Now
suppose that Q sues some unrelated party R for patent infringement
about some unrelated program Z and triggers the mutual defense clause.

If the license for X+W is the GPL, this patent suit has no effect on
Q's right to use X+W.  Q can still use it--or any part of it--under
the GPL.  However, if the mutual defense clause applies to X+W, then Q
loses the right to distribute X+W and could be sued for copyright
infringement for using (parts of) that work in a way that he has no
copyright license for.  That means that the conditions on use of X+W
are different from the GPL.  The GPL does not permit using W in such a
combination.

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