\chapter{The GNU General Public License}\label{GNU-GPL}

\centerline{\bf GNU GENERAL PUBLIC LICENSE}
\centerline{Version 2, June 1991}

Copyright \copyright\ 1989, 1991 Free Software Foundation, Inc.  675
Mass Ave, Cambridge, MA 02139, USA

Everyone is permitted to copy and distribute verbatim copies of this
license document, but changing it is not allowed.

\section*{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 Library 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.

\section*{Terms and Conditions}

\begin{enumerate}
\setcounter{enumi}{-1}
\item 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.
  
\item 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.
  
\item 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:

\begin{enumerate}
\item[a.]  You must cause the modified files to carry prominent
  notices stating that you changed the files and the date of any
  change.
  
\item[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.
  
\item[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.)
\end{enumerate}

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.

\item 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:

\begin{enumerate}
\item[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,
  
\item[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,
  
\item[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.)
\end{enumerate}

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.

\item 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.
  
\item 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.
  
\item 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.
  
\item 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.
  
\item 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.
  
\item 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.
  
\item 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.
\end{enumerate}

\section*{NO WARRANTY}

\begin{enumerate}
  \setcounter{enumi}{10}
\item 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.
  
\item 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.
\end{enumerate}

\section*{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.

\begin{quote}
  {\em one line to give the program's name and an idea of what it does.}\\
  Copyright \copyright\ 19{\em yy\/} {\em 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., 675 Mass Ave, Cambridge, MA 02139,
\end{quote}

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:

\begin{quote}
  Gnomovision version 69, Copyright \copyright\ 19{\em yy} {\em 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.
\end{quote}

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:

\begin{quote}
  Yoyodyne, Inc., hereby disclaims all copyright interest in the
  program `Gnomovision' (which makes passes at compilers) written by
  James Hacker.
  

  {\em signature of Ty Coon}, 1 April 1989\\
  Ty Coon, President of Vice
\end{quote}

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 Library General Public License instead of this License.
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