of the domain of the copyright system.  A copyright holder can often

\defn{disclaim} their copyright. (For example, under USA copyright law

it is possible for a copyright holder to engage in conduct resulting

in abandonment of copyright.)  If copyright is disclaimed, the software is

effectively no longer restricted by copyright law.   Software not restricted by copyright is in the

``public domain.''

\subsection{Public Domain Software}

In the USA and other countries that

are parties to the Berne Convention on Copyright, software is copyrighted

automatically by the author when she fixes the software in a tangible

medium.  In the software world, this usually means typing the source code

of the software into a file.

Imagine if authors could truly disclaim those default controls of copyright

law.  If so, the software is in the public domain --- no longer covered by

copyright.  Since copyright law is the construction allowing for most

restrictions on software (i.e., prohibition of copying, modification, and

redistribution), removing the software from the copyright system usually

yields software freedom for its users.

Carefully note that software truly in the public domain is \emph{not} licensed

in any way.  It is confusing to say software is ``licensed for the

public domain,'' or any phrase that implies the copyright holder gave

express permission to take actions governed by copyright law.

Copyright holders who state that they are releasing their code into

the public domain are effectively renouncing copyright controls on

the work.  The law gave the copyright holders exclusive controls over the

work, and they chose to waive those controls.  Software that is, in

this sense, in the public domain

is conceptualized by the developer as having no copyright and thus no license. The software freedoms discussed in

Section~\ref{Free Software Definition} are all granted because there is no

legal system in play to take them away.

Admittedly, a discussion of public domain software is an oversimplified

example.  

Because copyright controls are usually automatically granted and because, in

some jurisdictions, some copyright controls cannot be waived (see

Section~\ref{non-usa-copyright} for further discussion), many copyright

holders sometimes incorrectly believe a work has been placed in the public

domain.  Second, due to aggressive lobbying by the entertainment industry,

the ``exclusive Right'' of copyright, that was supposed to only exist for

``Limited Times'' according to the USA Constitution, appears to be infinite:

simply purchased on the installment plan rather than in whole.  Thus, we must

assume no works of software will fall into the public domain merely due to

the passage of time.

Nevertheless, under USA law it is likely that the typical

disclaimers of copyright or public domain dedications we see in the

Free Software world would be interpreted by courts as copyright

abandonment, leading to a situation in which the user effectively receives a

maximum grant of copyright freedoms, similar to a maximally-permissive

Free Software license.

The best example of software known to truly be in the public domain is software

that is published by the USA government.  Under

\href{http://www.law.cornell.edu/uscode/text/17/105}{17 USC 101 \S~105}, all

works published by the USA Government are not copyrightable in the USA.

\subsection{Why Copyright Free Software?}

If simply disclaiming copyright on software yields Free Software, then it

stands to reason that putting software into the public domain is the

easiest and most straightforward way to produce Free Software. Indeed,

some major Free Software projects have chosen this method for making their

software Free. However, most of the Free Software in existence \emph{is}

copyrighted. In most cases (particularly in those of FSF and the GNU

Project), this was done due to very careful planning.

Software released into the public domain does grant freedom to those users

who receive the standard versions on which the original author disclaimed

copyright. However, since the work is not copyrighted, any nontrivial

modification made to the work is fully copyrightable.

Free Software released into the public domain initially is Free, and

perhaps some who modify the software choose to place their work into the

public domain as well. However, over time, some entities will choose to

proprietarize their modified versions. The public domain body of software

feeds the proprietary software. The public commons disappears, because

fewer and fewer entities have an incentive to contribute back to the

commons. They know that any of their competitors can proprietarize their

enhancements. Over time, almost no interesting work is left in the public

domain, because nearly all new work is done by proprietarization.

A legal mechanism is needed to redress this problem. FSF was in fact

originally created primarily as a legal entity to defend software freedom,

and that work of defending software freedom is a substantial part of

its work today. Specifically because of this ``embrace, proprietarize and

extend'' cycle, FSF made a conscious choice to copyright its Free Software,

and then license it under ``copyleft'' terms. Many, including the

developers of the kernel named Linux, have chosen to follow this paradigm.

\label{copyleft-definition}

Copyleft,

which uses functional parts of copyright law to achieve an unusual result

(legal protection for free sharing) forms the core legal principle of these

licenses. It modifies, or ``hacks'' copyright law, which is usually employed to

strengthen the rights of authors or publishers, to strengthen instead the

rights of users.   %FIXME-URGENT: end

Copyleft is a legal strategy and mechanism to defend, uphold and propagate software

freedom. The basic technique of copyleft is as follows: copyright the

software, license it under terms that give all the software freedoms, but

use the copyright law controls to ensure that all who receive a copy of

the software have equal rights and freedom. In essence, copyleft grants

freedom, but forbids others to forbid that freedom to anyone else along

the distribution and modification chains.

% FIXME-URGENT: integrate

This ``reciprocity'' or ``share and share alike'' rule protects both

developers, who avoid facing a ``proprietized'' competitor of their project,

and users, who can be sure that they will have all four basic freedoms not

only in the present version of the program they use, but in all its future

improved versions.

% FIXME-URGENT: integrate

The unit of copyright law is ``the work''. In that sense, the ``work''

referenced by the licenses is anything that can be copyrighted or will be

subject to the terms of copyright law. The GNU licenses exercise their scope

fully. Anything which is ``a work'' or a ``work based on a work'' licensed

under GPL is subject to its requirements, including the requirement of

complete and corresponding source code, unless it is specifically

excepted. This principle often causes theoretical or speculative dispute

among lawyers, because ``the work'' is not a unit of computer programming. In

order to determine whether a ``routine'' an ``object'', a ``function'', a

``library'' or any other unit of software is part of one ``work'' when combined

with other GPL’d code, we must ask a question that copyright law will not

directly answer in the same technical terms.

The key here is that the GNU GPL licenses mean to ``plow fence row to fence

row'', covering every version of ``work based on the work'' recognized by local

copyright law, but no further.

%FIXME-URGENT: end

Copyleft is a general concept. Much like ideas for what a computer might

do must be \emph{implemented} by a program that actually does the job, so

too must copyleft be implemented in some concrete legal structure.

``Share and share alike'' is a phrase that is used often enough to explain the

concept behind copyleft, but to actually make it work in the real world, a

true implementation in legal text must exist. The GPL is the primary

implementation of copyleft in copyright licensing language.

\subsection{Software and Non-Copyright Legal Regimes}

\label{software-and-non-copyright}

The use, modification and distribution of software, like many endeavors,

simultaneously interacts with multiple different legal regimes.  As was noted

early via footnotes, copyright is merely the \textit{most common way} to

restrict users' rights to copy, share, modify and/or redistribute software.

However, proprietary software licenses typically use every mechanism

available to subjugate users.  For example:

\begin{itemize}

\item Unfortunately, despite much effort by many in the software freedom

  community to end patents that read on software (i.e., patents on

  computational ideas), they still ultimately exist.  As such, a software

  program might otherwise be seemly unrestricted, but a patent might read on

  the software and ruin everything for its users.\footnote{See

  \S\S~\ref{gpl-implied-patent-grant},~\ref{GPLv2s7},~\ref{GPLv3s11} for more

  discussion on how the patent system interacts with copyleft, and read

  Richard M.~Stallman's essay,

  \href{http://www.wired.com/opinion/2012/11/richard-stallman-software-patents/}{\textit{Let's

      Limit the Effect of Software Patents, Since We Can't Eliminate Them}}

  for more information on the problems these patents present to society.}

\item Digital Restrictions Management (usually called \defn{DRM}) is often

  used to impose technological restrictions on users' ability to exercise

  software freedom that they might otherwise be granted\footnote{See

    \S~\ref{GPLv3-drm} for more information on how GPL deals with this issue.}.

  The simplest (and perhaps oldest) form of DRM, of course, is separating

  software source code (read by humans), from their compiled binaries (read

  only by computers).  Furthermore,

  \href{http://www.law.cornell.edu/uscode/text/17/1201}{17 USC~\S1201} often

  prohibits users legally from circumventing some of these DRM systems.

\item Most EULAs also include a contractual agreement that bind users further

  by forcing them to agree to a contractual, prohibitive software license

  before ever even using the software.

\end{itemize}

Thus, most proprietary software restricts users via multiple interlocking

legal and technological means.  Any license that truly respect the software

freedom of all users must not only grant appropriate copyright permissions,

but also \textit{prevent} restrictions from other legal and technological

means like those listed above.

  If you wish to incorporate parts of the library into other Free programs

  whose distribution conditions are incompatible with these, 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.

\begin{center}

{\Large\sc

No Warranty

}

\end{center}

\item

{\sc Because the library is licensed free of charge, there is no

warranty for the library, to the extent permitted by applicable law.

Except when otherwise stated in writing the copyright holders and/or

other parties provide the library ``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

library is with you. should the library prove defective, you assume

the cost of all necessary servicing, repair or correction.}

% \pagebreak[4]

\item

{\sc 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 library 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 library

  (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 library to operate with any other software), even if such holder or

  other party has been advised of the possibility of such damages.}

\end{enumerate}

\begin{center}

{\Large\sc End of Terms and Conditions}

\end{center}

\vfill

\pagebreak[4]

\section*{How to Apply These Terms to Your New Libraries}

If you develop a new library, and you want it to be of the greatest

possible use to the public, we recommend making it Free Software that

everyone can redistribute and change. You can do so by permitting

redistribution under these terms (or, alternatively, under the terms of

the ordinary General Public License).

To apply these terms, attach the following notices to the library. 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}

one line to give the library's name and a brief idea of what it does. \\

Copyright (C) year  name of author \\

This library is Free Software; you can redistribute it and/or modify it

under the terms of the GNU Lesser General Public License as published by

the Free Software Foundation; either version 2.1 of the License, or (at

your option) any later version.

This library 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 Lesser General Public

License for more details.

You should have received a copy of the GNU Lesser General Public License

along with this library; if not, write to the Free Software Foundation,

Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA

\end{quote}

Also add information on how to contact you by electronic and paper mail.

You should also get your employer (if you work as a programmer) or your

school, if any, to sign a ``copyright disclaimer'' for the library, 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. \\

signature of Ty Coon, 1 April 1990 \\

Ty Coon, President of Vice

\end{quote}

\chapter{The GNU General Public License, version 3}

\begin{center}

{\parindent 0in

Version 3, 29 June 2007

Copyright \copyright\  2007 Free Software Foundation, Inc. \texttt{http://fsf.org/}

\bigskip

Everyone is permitted to copy and distribute verbatim copies of this

license document, but changing it is not allowed.}

\end{center}

\begin{center}

{\bf\large Preamble}

\end{center}

The GNU General Public License is a free, copyleft license for

software and other kinds of works.

The licenses for most software and other practical works are designed

to take away your freedom to share and change the works.  By contrast,

the GNU General Public License is intended to guarantee your freedom to

share and change all versions of a program--to make sure it remains free

software for all its users.  We, the Free Software Foundation, use the

GNU General Public License for most of our software; it applies also to

any other work released this way by its authors.  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

them 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 prevent others from denying you

these rights or asking you to surrender the rights.  Therefore, you have

certain responsibilities if you distribute copies of the software, or if

you modify it: responsibilities to respect the freedom of others.

For example, if you distribute copies of such a program, whether

gratis or for a fee, you must pass on to the recipients the same

freedoms that you received.  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.

Developers that use the GNU GPL protect your rights with two steps:

(1) assert copyright on the software, and (2) offer you this License

giving you legal permission to copy, distribute and/or modify it.

For the developers' and authors' protection, the GPL clearly explains

that there is no warranty for this free software.  For both users' and

authors' sake, the GPL requires that modified versions be marked as

changed, so that their problems will not be attributed erroneously to

authors of previous versions.

Some devices are designed to deny users access to install or run

modified versions of the software inside them, although the manufacturer

can do so.  This is fundamentally incompatible with the aim of

protecting users' freedom to change the software.  The systematic

pattern of such abuse occurs in the area of products for individuals to

use, which is precisely where it is most unacceptable.  Therefore, we

have designed this version of the GPL to prohibit the practice for those

products.  If such problems arise substantially in other domains, we

stand ready to extend this provision to those domains in future versions

of the GPL, as needed to protect the freedom of users.

Finally, every program is threatened constantly by software patents.

States should not allow patents to restrict development and use of

software on general-purpose computers, but in those that do, we wish to

avoid the special danger that patents applied to a free program could

make it effectively proprietary.  To prevent this, the GPL assures that

patents cannot be used to render the program non-free.

The precise terms and conditions for copying, distribution and

modification follow.

\begin{center}

{\Large \sc Terms and Conditions}

\end{center}

\begin{enumerate}

\addtocounter{enumi}{-1}

\item Definitions.

``This License'' refers to version 3 of the GNU General Public License.

``Copyright'' also means copyright-like laws that apply to other kinds of

works, such as semiconductor masks.

``The Program'' refers to any copyrightable work licensed under this