This library is free; this means that everyone is free to use it and free to redistribute it on a free basis. The library is not in the public domain; it is copyrighted and there are restrictions on its distribution, but these restrictions are designed to permit everything that a good cooperating citizen would want to do. What is not allowed is to try to prevent others from further sharing any version of this library that they might get from you.
Specifically, we want to make sure that you have the right to give away copies of the library, that you receive source code or else can get it if you want it, that you can change this library or use pieces of it in new free programs, and that you know you can do these things.
To make sure that everyone has such rights, we have to forbid you to deprive anyone else of these rights. For example, if you distribute copies of the GNU MP library, you must give the recipients all the rights that you have. You must make sure that they, too, receive or can get the source code. And you must tell them their rights.
Also, for our own protection, we must make certain that everyone finds out that there is no warranty for the GNU MP library. If it is modified by someone else and passed on, we want their recipients to know that what they have is not what we distributed, so that any problems introduced by others will not reflect on our reputation.
More precisely, the GNU MP library is dual licensed, under the conditions of the GNU Lesser General Public License version 3 (see COPYING.LESSERv3), or the GNU General Public License version 2 (see COPYINGv2). This is the recipient’s choice, and the recipient also has the additional option of applying later versions of these licenses. (The reason for this dual licensing is to make it possible to use the library with programs which are licensed under GPL version 2, but which for historical or other reasons do not allow use under later versions of the GPL.)
Programs which are not part of the library itself, such as demonstration programs and the GMP testsuite, are licensed under the terms of the GNU General Public License version 3 (see COPYINGv3), or any later version.