.. _gpl:

.. index::
   pair: license; GPL

GNU GENERAL PUBLIC LICENSE
==========================

Version 2, June 1991

::

    
         Copyright © 1989, 1991 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.
    
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Preamble
````````

The licenses for most software are designed to take away your freedom to share and
change it. By contrast, the GNU General Public License is intended to guarantee your
freedom to share and change free software—to make sure the software is free for all
its users. This General Public License applies to most of the Free Software
Foundation's software and to any other program whose authors commit to using it.
(Some other Free Software Foundation software is covered by the GNU Lesser General
Public License instead.) You can apply it to your programs, too.

When we speak of free software, we are referring to freedom, 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 or use
pieces of it in new free programs; and that you know you can do these things.

To protect your rights, we need to make restrictions that forbid anyone to deny you
these rights or to ask you to surrender the rights. These restrictions translate to
certain responsibilities for you if you distribute copies of the software, or if you
modify it.

For example, if you distribute copies of such a program, whether gratis or for a
fee, 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 show them these
terms so they know their rights.

We protect your rights with two steps: (1) copyright the software, and (2) offer you
this license which gives you legal permission to copy, distribute and/or modify the
software.

Also, for each author's protection and ours, we want to make certain that everyone
understands that there is no warranty for this free software. If the software is
modified by someone else and passed on, we want its recipients to know that what
they have is not the original, so that any problems introduced by others will not
reflect on the original authors' reputations.

Finally, any free program is threatened constantly by software patents. We wish to
avoid the danger that redistributors of a free program will individually obtain
patent licenses, in effect making the program proprietary. To prevent this, we have
made it clear that any patent must be licensed for everyone's free use or not
licensed at all.

The precise terms and conditions for copying, distribution and modification follow.

TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION
```````````````````````````````````````````````````````````````

1.  This License applies to any program or other work which contains a notice placed
    by the copyright holder saying it may be distributed under the terms of this
    General Public License. The “Program”, below, refers to any such program or
    work, and a “work based on the Program” means either the Program or any
    derivative work under copyright law: that is to say, a work containing the
    Program or a portion of it, either verbatim or with modifications and/or
    translated into another language. (Hereinafter, translation is included without
    limitation in the term “modification”.) Each licensee is addressed as “you”.

    Activities other than copying, distribution and modification are not covered by
    this License; they are outside its scope. The act of running the Program is not
    restricted, and the output from the Program is covered only if its contents
    constitute a work based on the Program (independent of having been made by
    running the Program). Whether that is true depends on what the Program does.

2.  You may copy and distribute verbatim copies of the Program's 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 of warranty;
    keep intact all the notices that refer to this License and to the absence of any
    warranty; and give any other recipients of the Program a copy of this License
    along with the Program.

    You may charge a fee for the physical act of transferring a copy, and you may at
    your option offer warranty protection in exchange for a fee.

3.  You may modify your copy or copies of the Program or any portion of it, thus
    forming a work based on the Program, and copy and distribute such modifications
    or work under the terms of Section 1 above, provided that you also meet all of
    these conditions:

    a.  You must cause the modified files to carry prominent notices stating that
        you changed the files and the date of any change.

    b.  You must cause any work that you distribute or publish, that in whole or in
        part contains or is derived from the Program or any part thereof, to be
        licensed as a whole at no charge to all third parties under the terms of
        this License.

    c.  If the modified program normally reads commands interactively when run, you
        must cause it, when started running for such interactive use in the most
        ordinary way, to print or display an announcement including an appropriate
        copyright notice and a notice that there is no warranty (or else, saying
        that you provide a warranty) and that users may redistribute the program
        under these conditions, and telling the user how to view a copy of this
        License. (Exception: if the Program itself is interactive but does not
        normally print such an announcement, your work based on the Program is not
        required to print an announcement.)

    These requirements apply to the modified work as a whole. If identifiable
    sections of that work are not derived from the Program, and can be reasonably
    considered independent and separate works in themselves, then this License, and
    its terms, do not apply to those sections when you distribute them as separate
    works. But when you distribute the same sections as part of a whole which is a
    work based on the Program, the distribution of the whole must be on the terms of
    this License, whose permissions for other licensees extend to the entire whole,
    and thus to each and every part regardless of who wrote it.

    Thus, it is not the intent of this section to claim rights or contest your
    rights to work written entirely by you; rather, the intent is to exercise the
    right to control the distribution of derivative or collective works based on the
    Program.

    In addition, mere aggregation of another work not based on the Program with the
    Program (or with a work based on the Program) on a volume of a storage or
    distribution medium does not bring the other work under the scope of this
    License.

4.  You may copy and distribute the Program (or a work based on it, under Section 2)
    in object code or executable form under the terms of Sections 1 and 2 above
    provided that you also do one of the following:

    a.  Accompany it with the complete corresponding machine-readable source code,
        which must be distributed under the terms of Sections 1 and 2 above on a
        medium customarily used for software interchange; or,

    b.  Accompany it with a written offer, valid for at least three years, to give
        any third party, for a charge no more than your cost of physically
        performing source distribution, a complete machine-readable copy of the
        corresponding source code, to be distributed under the terms of Sections 1
        and 2 above on a medium customarily used for software interchange; or,

    c.  Accompany it with the information you received as to the offer to distribute
        corresponding source code. (This alternative is allowed only for
        noncommercial distribution and only if you received the program in object
        code or executable form with such an offer, in accord with Subsection b
        above.)

    The source code for a work means the preferred form of the work for making
    modifications to it. For an executable work, complete source code means all the
    source code for all modules it contains, plus any associated interface
    definition files, plus the scripts used to control compilation and installation
    of the executable. However, as a special exception, the source code distributed
    need not include anything that is normally distributed (in either source or
    binary form) with the major components (compiler, kernel, and so on) of the
    operating system on which the executable runs, unless that component itself
    accompanies the executable.

    If distribution of executable or object code is made by offering access to copy
    from a designated place, then offering equivalent access to copy the source code
    from the same place counts as distribution of the source code, even though third
    parties are not compelled to copy the source along with the object code.

5.  You may not copy, modify, sublicense, or distribute the Program except as
    expressly provided under this License. Any attempt otherwise to copy, modify,
    sublicense or distribute the Program is void, and will automatically terminate
    your rights under this License. However, parties who have received copies, or
    rights, from you under this License will not have their licenses terminated so
    long as such parties remain in full compliance.

6.  You are not required to accept this License, since you have not signed it.
    However, nothing else grants you permission to modify or distribute the Program
    or its derivative works. These actions are prohibited by law if you do not
    accept this License. Therefore, by modifying or distributing the Program (or any
    work based on the Program), you indicate your acceptance of this License to do
    so, and all its terms and conditions for copying, distributing or modifying the
    Program or works based on it.

7.  Each time you redistribute the Program (or any work based on the Program), the
    recipient automatically receives a license from the original licensor to copy,
    distribute or modify the Program subject to these terms and conditions. You may
    not impose any further restrictions on the recipients' exercise of the rights
    granted herein. You are not responsible for enforcing compliance by third
    parties to this License.

8.  If, as a consequence of a court judgment or allegation of patent infringement or
    for any other reason (not limited to patent issues), conditions are imposed on
    you (whether by court order, agreement or otherwise) that contradict the
    conditions of this License, they do not excuse you from the conditions of this
    License. If you cannot distribute so as to satisfy simultaneously your
    obligations under this License and any other pertinent obligations, then as a
    consequence you may not distribute the Program at all. For example, if a patent
    license would not permit royalty-free redistribution of the Program by all those
    who receive copies directly or indirectly through you, then the only way you
    could satisfy both it and this License would be to refrain entirely from
    distribution of the Program.

    If any portion of this section is held invalid or unenforceable under any
    particular circumstance, the balance of the section is intended to apply and the
    section as a whole is intended to apply in other circumstances.

    It is not the purpose of this section to induce you to infringe any patents or
    other property right claims or to contest validity of any such claims; this
    section has the sole purpose of protecting the integrity of the free software
    distribution system, which is implemented by public license practices. Many
    people have made generous contributions to the wide range of software
    distributed through that system in reliance on consistent application of that
    system; it is up to the author/donor to decide if he or she is willing to
    distribute software through any other system and a licensee cannot impose that
    choice.

    This section is intended to make thoroughly clear what is believed to be a
    consequence of the rest of this License.

9.  If the distribution and/or use of the Program is restricted in certain countries
    either by patents or by copyrighted interfaces, the original copyright holder
    who places the Program under this License may add an explicit geographical
    distribution limitation excluding those countries, so that distribution is
    permitted only in or among countries not thus excluded. In such case, this
    License incorporates the limitation as if written in the body of this License.

10. The Free Software Foundation may publish revised and/or new versions of the
    General Public License from time to time. Such new versions will be similar in
    spirit to the present version, but may differ in detail to address new problems
    or concerns.

    Each version is given a distinguishing version number. If the Program specifies
    a version number of this License which applies to it and “any later version”,
    you have the option of following the terms and conditions either of that version
    or of any later version published by the Free Software Foundation. If the
    Program does not specify a version number of this License, you may choose any
    version ever published by the Free Software Foundation.

11. If you wish to incorporate parts of the Program into other free programs whose
    distribution conditions are different, write to the author to ask for
    permission. For software which is copyrighted by the Free Software Foundation,
    write to the Free Software Foundation; we sometimes make exceptions for this.
    Our decision will be guided by the two goals of preserving the free status of
    all derivatives of our free software and of promoting the sharing and reuse of
    software generally.

12. BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY FOR THE
    PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT WHEN OTHERWISE STATED
    IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM “AS
    IS” WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT
    NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
    PARTICULAR PURPOSE. THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE
    PROGRAM IS WITH YOU. SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF
    ALL NECESSARY SERVICING, REPAIR OR CORRECTION.

13. IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING WILL ANY
    COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR REDISTRIBUTE THE
    PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY GENERAL,
    SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OR INABILITY
    TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF DATA OR DATA BEING
    RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD PARTIES OR A FAILURE OF
    THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS), EVEN IF SUCH HOLDER OR OTHER
    PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.

Appendix: How to Apply These Terms to Your New Programs
```````````````````````````````````````````````````````

If you develop a new program, and you want it to be of the greatest possible use to
the public, the best way to achieve this is to make it free software which everyone
can redistribute and change under these terms.

To do so, attach the following notices to the program. It is safest to attach them
to the start of each source file to most effectively convey the exclusion of
warranty; and each file should have at least the “copyright” line and a pointer to
where the full notice is found.

::

    
         one line to give the program's name and a brief idea of what it does.
         Copyright (C) yyyy  name of author
         
         This program is free software; you can redistribute it and/or modify
         it under the terms of the GNU General Public License as published by
         the Free Software Foundation; either version 2 of the License, or
         (at your option) any later version.
         
         This program is distributed in the hope that it will be useful,
         but WITHOUT ANY WARRANTY; without even the implied warranty of
         MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
         GNU General Public License for more details.
         
         You should have received a copy of the GNU General Public License
         along with this program; if not, write to the Free Software
         Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
    
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Also add information on how to contact you by electronic and paper mail.

If the program is interactive, make it output a short notice like this when it
starts in an interactive mode:

::

    
         Gnomovision version 69, Copyright (C) year name of author
         Gnomovision comes with ABSOLUTELY NO WARRANTY; for details type 'show w'.
         This is free software, and you are welcome to redistribute it
         under certain conditions; type 'show c' for details.
    
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The hypothetical commands 'show w' and 'show c' should show the appropriate parts of
the General Public License. Of course, the commands you use may be called something
other than 'show w' and 'show c'; they could even be mouse-clicks or menu
items—whatever suits your program.

You should also get your employer (if you work as a programmer) or your school, if
any, to sign a “copyright disclaimer” for the program, if necessary. Here is a
sample; alter the names:

::

    
         Yoyodyne, Inc., hereby disclaims all copyright interest in the program
         'Gnomovision' (which makes passes at compilers) written by James Hacker.
         
         signature of Ty Coon, 1 April 1989
         Ty Coon, President of Vice
    
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This General Public License does not permit incorporating your program into
proprietary programs. If your program is a subroutine library, you may consider it
more useful to permit linking proprietary applications with the library. If this is
what you want to do, use the GNU Lesser General Public License instead of this
License.
