GNU GENERAL PUBLIC LICENSE
Version 3, 29 June 2007
Copyright © 2007 Free Software Foundation, Inc.
Permission is granted to copy and distribute verbatim copies of this license document, but modification is not permitted.
Introduction
The GNU General Public License is a free, copyleft license for software and other similar works.
Most software and other experimental works licenses are designed to take away your freedom to share and change the work. In contrast, the GNU General Public License is intended to guarantee your freedom to share and change all versions of the program - to ensure that 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 also applies to any other work released in this way by its authors. You can apply it to your programs as well.
When we talk about free software, we're talking about 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 want), that you can receive the source code or get it if you want, 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 must prevent others from denying you these rights or asking you to give up rights. Therefore, if you distribute copies of the software or if you modify it, you have certain responsibilities: Responsibilities to respect the freedoms of others.
For example, if you distribute copies of such a program, either free of charge or for a fee, you must pass on to the recipients the same freedoms you have received. You must ensure that they also receive or can obtain the source code. And you must show them these terms so that they know their rights.