8
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
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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
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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 nonfree programs. These disadvantages are the reason we
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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 nonfree 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
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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.
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