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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 fi ts 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.
Although the Lesser General Public License is Less protective of the users’ freedom, it does ensure that the user of
a program that is linked with the Library has the freedom and the wherewithal to run that program using a modifi ed
version of the Library.
The precise terms and conditions for copying, distribution and modifi cation follow. Pay close attention to the difference
between a “work based on the library” and a “work that uses the library”. The former contains code derived from the
library, whereas the latter must be combined with the library in order to run.
GNU LESSER GENERAL PUBLIC LICENSE
TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION
0. This License Agreement applies to any software library or other program which contains a notice placed by the
copyright holder or other authorized party saying it may be distributed under the terms of this Lesser General Public
License (also called “this License”). Each licensee is addressed as “you”.
A “library” means a collection of software functions and/or data prepared so as to be conveniently linked with application
programs (which use some of those functions and data) to form executables.
The “Library”, below, refers to any such software library or work which has been distributed under these terms. A
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containing the Library or a portion of it, either verbatim or with modifi cations and/or translated straightforwardly into
another language. (Hereinafter, translation is included without limitation in the term “modifi cation”.)
“Source code” for a work means the preferred form of the work for making modifi cations to it. For a library, complete
source code means all the source code for all modules it contains, plus any associated interface defi nition fi les, plus the
scripts used to control compilation and installation of the library.
Activities other than copying, distribution and modifi cation are not covered by this License; they are outside its scope.
The act of running a program using the Library is not restricted, and output from such a program is covered only if its
contents constitute a work based on the Library (independent of the use of the Library in a tool for writing it). Whether
that is true depends on what the Library does and what the program that uses the Library does.
1. You may copy and distribute verbatim copies of the Library’s complete source code as you receive it, in any medium,
provided that you conspicuously and appropriately publish on each copy an appropriate copyright notice and disclaimer
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copy of this License along with the Library.
You may charge a fee for the physical act of transferring a copy, and you may at your option offer warranty protection
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copy and distribute such modifi cations or work under the terms of Section 1 above, provided that you also meet all of
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License.
d) If a facility in the modifi ed Library refers to a function or a table of data to be supplied by an application program that
uses the facility, other than as an argument passed when the facility is invoked, then you must make a good faith
effort to ensure that, in the event an application does not supply such function or table, the facility still operates, and
performs whatever part of its purpose remains meaningful.
(For example, a function in a library to compute square roots has a purpose that is entirely well-defi ned independent of
the application. Therefore, Subsection 2d requires that any application-supplied function or table used by this function
must be optional: if the application does not supply it, the square root function must still compute square roots.)