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13. GNU GENERAL PUBLIC LICENSE
Version 3, 29 June 2007
Copyright © 2007 Free Software Foundation, Inc. <http://fsf.org/>
Everyone is permitted to copy and distribute verbatim copies of this license document,
but changing it is not allowed.
Pre a m ble
The GNU General Public License is a free, copyleft license for software and other kinds
of works.
The licenses for most software and other practical works are designed to take away
your freedom to share and change the works. By contrast, the GNU General Public
License is intended to guarantee your freedom to share and change all versions of a
program--to make sure it remains free software for all its users. We, the Free Software
Foundation, use the GNU General Public License for most of our software; it applies also
to any other work released this way by its authors. You can apply it to your programs,
too.
When we speak of free software, we are referring to freedom, not price. Our General
Public Licenses are designed to make sure that you have the freedom to distribute
copies of free software (and charge for them if you wish), that you receive source
code or can get it if you want it, that you can change the software or use pieces of it
in new free programs, and that you know you can do these things.
To protect your rights, we need to prevent others from denying you these rights or
asking you to surrender the rights. Therefore, you have certain responsibilities if you
distribute copies of the software, or if you modify it: responsibilities to respect the
freedom of others.
For example, if you distribute copies of such a program, whether gratis or for a fee, you
must pass on to the recipients the same freedoms that you received. You must make
sure that they, too, receive or can get the source code. And you must show them
these terms so they know their rights.
