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GNU LESSER GENERAL PUBLIC LICENSE
Version 2.1, February 1999
Copyright (C) 1991, 1999 Free Software Foundation, Inc. 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301
USA Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not
allowed.
[This is the first released version of the Lesser GPL. It also counts as the successor of the GNU Library Public
License, version 2, hence the version number 2.1.]
Preamble
The licenses for most software are designed to take away your freedom to share and change it. By contrast, the GNU
General Public Licenses are intended to guarantee your freedom to share and change free software--to make sure the
software is free for all its users.
This license, the Lesser General Public License, applies to some specially designated software packages--typically
libraries--of the Free Software Foundation and other authors who decide to use it. You can use it too, but we suggest
you first think carefully about whether this license or the ordinary General Public License is the better strategy to use in
any particular case, based on the explanations below.
When we speak of free software, we are referring to freedom of use, 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 this service if you
wish); that you receive source code or can get it if you want it; that you can change the software and use pieces of
it in new free programs; and that you are informed that you can do these things.
To protect your rights, we need to make restrictions that forbid distributors to deny you these rights or to ask you to
surrender these rights. These restrictions translate to certain responsibilities for you if you distribute copies of the
library or if you modify it.
For example, if you distribute copies of the library, whether gratis or for a fee, you must give the recipients all the
rights that we gave you. You must make sure that they, too, receive or can get the source code. If you link other code
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after making changes to the library and recompiling it. And you must show them these terms so they know their rights.
We protect your rights with a two-step method: (1) we copyright the library, and (2) we offer you this license, which
gives you legal permission to copy, distribute and/or modify the library.
To protect each distributor, we want to make it very clear that there is no warranty for the free library. Also, if the
library is modified by someone else and passed on, the recipients should know that what they have is not the original
version, so that the original author's reputation will not be affected by problems that might be introduced by others.
Finally, software patents pose a constant threat to the existence of any free program. We wish to make sure that a
company cannot effectively restrict the users of a free program by obtaining a restrictive license from a patent holder.
Therefore, we insist that any patent license obtained for a version of the library must be consistent with the full freedom
of use specified in this license.
Most GNU software, including some libraries, is covered by the ordinary GNU General Public License. This license,
the GNU Lesser General Public License, applies to certain designated libraries, and is quite different from the ordinary
General Public License. We use this license for certain libraries in order to permit linking those libraries into non-free
programs.
When a program is linked with a library, whether statically or using a shared library, the combination of the two is
legally speaking a combined work, a derivative of the original library. The ordinary General Public License therefore
permits such linking only if the entire combination fits its criteria of freedom. The Lesser General Public License permits
more lax criteria for linking other code with the library.
We call this license the "Lesser" General Public License because it does Less to protect the user's freedom than the
ordinary General Public License. It also provides other free software developers Less of an advantage over competing
non-free programs. These disadvantages are the reason we use the ordinary General Public License for many
libraries. However, the Lesser license provides advantages in certain special circumstances.
For example, on rare occasions, there may be a special need to encourage the widest possible use of a certain library,
so that it becomes a de-facto standard. To achieve this, non-free programs must be allowed to use the library. A more
frequent case is that a free library does the same job as widely used non-free libraries. In this case, there is little to
gain by limiting the free library to free software only, so we use the Lesser General Public License.
In other cases, permission to use a particular library in non-free programs enables a greater number of people to use
a large body of free software. For example, permission to use the GNU C Library in non-free programs enables many
more people to use the whole GNU operating system, as well as its variant, the GNU/Linux operating system.
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