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The reason we have a separate publi c license for some libraries i s that they blur the dis-
tinction we usually make between mod ifying or adding to a program and simply using
it. Linking a program with a library, without changing the library, is in some sense sim-
ply using the library, and is analogous to running a ut ility program or application pro-
gram. However, in a textual and legal sense, the linked executable is a combined work,
a derivative of the original library, and the ordinary Gen eral Public License treats it as
such.
Because of this blurred distinction, using the ordinary General Public License for librar-
ies did not effectively promote software sharing, because most dev elopers did not use
the libraries. We concluded that weaker conditions might promote sharing better.
However, unrestricted linking of non-free programs would deprive the use rs of those
programs of all benefit from the free status of the libraries themselves. This Library Gen-
eral Public License is intended to permit developers of non-free programs to use free li-
braries, while preserving your freedom as a user of such programs to change the free
libraries that are incorporated in them. (We have not seen how to achieve this as rega rds
changes in header files, but we have achieved it as regards c hanges in the actual func-
tions of the Library.) The hope is that this will lead to faster development of free librar-
ies.
The precise terms and conditions for copying, distribution and modification 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, while the latter
only works together with the library.
Note that it is possible for a library to be covered by the ordinary Genera l Public License
rather than by this special one.
Terms and Conditions for Copying, Distribution and Modification
0. This License Agreement applies to any software library which contains a notice
placed by the copyright hol der or other authoriz ed party saying it may be
distributed under the terms of this Library General Pub lic 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 “work based on the Library” means either the
Library or any derivative work under copyright law: that is to say, a work
containing the Library or a portion of it, either verb atim or with modifications and/
or translated straightforwardly into another language. (Here inafter, translation is
included without limitation in the term “modification”.)
“Source code” for a work means the preferre d form of the work for making
modifications to it. For a library, complete s ource code means all the so urce code for
all modules it contains, plus any associated interface definitio n files, plus the scripts
used to control compilation and installation of the library.
Activities other than copying, distribution and modification 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 i s 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 Libr ary does and what
the program that uses the Library does.