[kelnos]

> GPLv3 clearly has no provisions to introduce arbitrary prohibitions into the license without losing compatibility.

It's not even just that. The license expressly forbids adding other conditions and restrictions, and says that people who receive software, licensed under the GPL, with added conditions ore restrictions, can just remove those restrictions.

If the author really wants to add a restriction like this, they have to switch to a different license.

[direwolf20]

Maybe they don't really want to add this restriction. Maybe they want a fig leaf, so when California asks them why they don't comply with the law, they can point to this and state it's not legal to use in California.