% For the moment, I've thrown in fancychap because I don't have time to

% research memoir.

% FIXME: Some overall formatting hacks that would really help:

%   * I have started using  \hyperref[LABEL]{text} extensively, which seems

%     to work great in the PDF and HTML versions, but in the Postscript

%     version, the link lost entirely.  I think we need an additional command

%     to replace \hyperref which takes an optional third argument that will

%     insert additional text only when generating print versions, such as:

%      \newhyperref[GPLv2s3]{the requirements for binary distribution under

%      GPLv2}{(see section~\ref*{GPLv2s3} for more information)}

%

%     This is a careful balance, because it'd be all too easy to over-pepper

%     the printed version with back/forward references, but there are

%     probably times when this is useful.

%   * Similar issue: \href{} is well known not to carry the URLs in the print

%     versions.  Adding a footnote with the URL for the print version is

%     probably right.  (or maybe a References page?)

%   * The text is extremely inconsistent regarding formatting of code and

%     commands.  The following varied different methods have been used:

%         + the \verb%..% inline form

%         + verbatim environment (i.e., \begin{verbatim}

%         + {\tt }

%         + \texttt{}

%         + the lstlisting environment (i.e., \begin{lstlisting}

%     These should be made consistent, using only two forms: one for line and

%     one for a long quoted section.

% FIXME: s/GPL enforcers/COGEOs/g

%        (the term coined later but not used throughout) This can't be done

%        by rote, since it may not be appropriate everywhere and shouldn't be

%        used *before* it's coined in the early portions of

%        compliance-guide.tex (and it's probably difficult to coin it earlier

%        anyway).  BTW, I admit COGEOs isn't the best acronym, but I started

%        with ``Community Enforcement Organizations'', which makes CEO, which

%        is worse. :)  My other opting was   COEO, which seemed too close to

%        CEO.  Suggestions welcome.

\usepackage{listings}

\usepackage{enumerate}

\usepackage{enumitem}

\usepackage[Conny]{fncychap}

\usepackage[dvips]{graphicx}

\usepackage[verbose, twoside, dvips,

              paperwidth=8.5in, paperheight=11in,

              left=1in, right=1in, top=1.25in, bottom=.75in,

           ]{geometry}

% Make sure hyperref is last in the package list.  Order matters here, See:

%   http://tex.stackexchange.com/questions/77886/fncychap-and-hyperref-messes-up-page-references

\usepackage{hyperref}

\newcommand{\tutorialpartsplit}[2]{#2}

%\input{no-numbers-on-table-of-contents}

\providecommand{\hrefnofollow}[2]{\href{#1}{#2}}

\hypersetup{pdfinfo={Title={Copyleft and the GNU General Public License: A Comprehensive Tutorial and Guide}}}

    \begin{document}

\pagestyle{plain}

\pagenumbering{roman}

\frontmatter

\begin{titlepage}

\begin{center}

{\Huge

{\sc Copyleft and the  \\

GNU General Public License:

\vspace{.25in}

A Comprehensive Tutorial \\

\vspace{.1in}

and Guide

}}

\vfill

{\parindent 0in

\begin{tabbing}

Copyright \= \copyright{} 2003--2005, 2008, 2014--2015, 2018 \hspace{1.mm} \=  \kill

Copyright \> \copyright{} 2018 \>  Chestek Legal. \\

Copyright \> \copyright{} 2014--2015 \>  Anthony K. Sebro, Jr. \\

Copyright \= \copyright{} 2014 \> Denver Gingerich. \\

Copyright \= \copyright{} 2003--2007, 2014 \>  Free Software Foundation, Inc. \\

Copyright \> \copyright{} 2008, 2014 \>  Software Freedom Law Center. \\

\end{tabbing}

\vspace{.3in}

The copyright holders grant the freedom to copy, modify, convey,

adapt, and/or redistribute this work (except

Appendices~\ref{GPLv2-full-text}--\ref{AGPLv3-full-text}) under the terms of the Creative Commons

Attribution Share Alike 4.0 International License.  A copy of that license is

available at \url{https://creativecommons.org/licenses/by-sa/4.0/legalcode}.

Appendices~\ref{GPLv2-full-text}--\ref{AGPLv3-full-text} include copies of the texts of various licenses published

by the FSF, and they are all licensed under the license, ``Everyone is permitted

to copy and distribute verbatim copies of this license document, but changing

it is not allowed.''.  However, those who seek to make modified versions of

those licenses should note the

\href{https://www.gnu.org/licenses/gpl-faq.html#ModifyGPL}{explanation given in the GPL FAQ}.

\vfill

As a public, collaborative project, this Guide is primarily composed of the

many contributions received via its

\href{https://k.copyleft.org/guide/files/master/CONTRIBUTING.md}{public

  contribution process}.  Please

\href{https://k.copyleft.org/guide/changelog/master/}{review its

  Git logs} for full documentation of all contributions, and

Appendix~\ref{third-party-citation-list}

  contains a list of third-party works from which some material herein was

adapted.

The most recent version is

available online at \url{https://copyleft.org/guide/}.  Patches

are indeed welcome to this material.  Sources can be found in the Git

repository at \url{https://k.copyleft.org/guide/}.

}

\end{center}

\end{titlepage}

\tableofcontents

\chapter{Preface}

This tutorial is the culmination of nearly a decade of studying and writing

about software freedom licensing and the GPL\@.  Each part of this tutorial

is a course unto itself, educating the reader on a myriad of topics from the

deep details of the GPLv2 and GPLv3, common business models in the copyleft

licensing area (both the friendly and unfriendly kind), best practices for

compliance with the GPL, for engineers, managers, and lawyers, as well as

real-world case studies of GPL enforcement matters.

It is unlikely that all the information herein is necessary to learn all at

once, and therefore this tutorial likely serves best as a reference book.

The material herein has been used as the basis for numerous live tutorials

and discussion groups since 2002, and the materials have been periodically

updated.   They likely stand on their own as excellent reference material.

However, if you are reading these course materials without attending a live

tutorial session, please note that this material is merely a summary of the

highlights of the various CLE and other tutorial courses based on this

material.  Please be aware that during the actual courses, class discussion

and presentation supplements this printed curriculum.  Simply reading this

material is \textbf{not equivalent} to attending a course.

\mainmatter

% FIXME: We need an Introduction.  I think ideally it goes here, before Part

%  I.  The introduction should cover initially:

%

%

%     * Why we cover the topics in the order that we do, in particular, why

%       we discuss all GPLv2 before mentioning  GPLv3 (i.e., explain why we

%       take a diachronic approach to study of GPL).

%

%     * It should briefly discuss Free Culture / Software Freedom stuff.

%       Maybe some early material currently living in gpl-lgpl.tex should move

%       to the introduction, maybe not.  The goal is to prepare for the

%       moment when we can merge in material about CC-BY-SA.

\input{gpl-lgpl}

\input{compliance-guide}

\input{enforcement-case-studies}

\appendix

\part{Appendices}

\input{third-party-citations}

\input{license-texts}

limited to the patent claims covered by the code as licensed by the patentee.

In contrast, a GPLv2 licensee, under the doctrine of implied patent license, 

is free to practice any patent claims held by the licensor that cover 

``reasonably contemplated uses'' of the GPL'd code, which may very well 

include creation and distribution of modified works since the GPL's terms, 

under which the patented code is distributed, expressly permits such activity.

Further supporting this result is the Federal Circuit's pronouncement that

the recipient of a patented article has, not only an implied license to

make, use, and sell the article, but also an implied patent license to

repair the article to enable it to function properly, Bottom Line Mgmt.,

Inc. v. Pan Man, Inc., 228 F.3d 1352 (Fed. Cir. 2000). Additionally, the

Federal Circuit extended that rule to include any future recipients of the

patented article, not just the direct recipient from the distributor.

This theory comports well with the idea of Free Software, whereby software

is distributed among many entities within the community for the purpose

of constant evolution and improvement. In this way, the law of implied

patent license used by the GPLv2 ensures that the community mutually

benefits from the licensing of patents to any single community member.

Note that simply because GPLv2'd software has an implied patent license does

not mean that any patents held by a distributor of GPLv2'd code become

worthless. To the contrary, the patents are still valid and enforceable

against either:

\begin{enumerate}

 \renewcommand{\theenumi}{\alph{enumi}}

 \renewcommand{\labelenumi}{\textup{(\theenumi)}}

\item any software other than that licensed under the GPLv2 by the patent

  holder, and

\item any party that does not comply with the GPLv2

with respect to the licensed software.

\end{enumerate}

\newcommand{\compB}{$\mathcal{B}$}

\newcommand{\compA}{$\mathcal{A}$}

For example, if Company \compA{} has a patent on advanced Web browsing, but

also licenses a Web browsing program under the GPLv2, then it

cannot assert the patent against any party based on that party's use of 

Company \compA{}'s GPL'd Web browsing software program, or on that party's

creation and use of modified versions of that GPL'd program.  However, if a

party uses that program without

complying with the GPLv2, then Company \compA{} can assert both copyright

infringement claims against the non-GPLv2-compliant party and

infringement of the patent, because the implied patent license only

extends to use of the software in accordance with the GPLv2. Further, if

Company \compB{} distributes a competitive advanced Web browsing program 

that is not a modified version of Company \compA{}'s GPL'd Web browsing software

program, Company \compA{} is free to assert its patent against any user or

distributor of that product. It is irrelevant whether Company \compB's

program is also distributed under the GPLv2, as Company \compB{} can not grant

implied licenses to Company \compA's patent.

This result also reassures companies that they need not fear losing their

proprietary value in patents to competitors through the GPLv2 implied patent

license, as only those competitors who adopt and comply with the GPLv2's

terms can benefit from the implied patent license. To continue the

example above, Company \compB{} does not receive a free ride on Company

\compA's patent, as Company \compB{} has not licensed-in and then

redistributed Company A's advanced Web browser under the GPLv2. If Company

\compB{} does do that, however, Company \compA{} still has not lost

competitive advantage against Company \compB{}, as Company \compB{} must then,

when it re-distributes Company \compA's program, grant an implied license

to any of its patents that cover the program. Further, if Company \compB{}

relicenses an improved version of Company A's program, it must do so under

the GPLv2, meaning that any patents it holds that cover the improved version

are impliedly licensed to any licensee. As such, the only way Company

\compB{} can benefit from Company \compA's implied patent license, is if it,

itself, distributes Company \compA's software program and grants an

implied patent license to any of its patents that cover that program.

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\chapter{Defending Freedom on Many Fronts}

Chapters~\ref{run-and-verbatim} and~\ref{source-and-binary} presented the

core freedom-defending provisions of GPLv2\@, which are in GPLv2~\S\S0--3.

GPLv2\S\S~4--7 of the GPLv2 are designed to ensure that GPLv2~\S\S0--3 are

not infringed, are enforceable, are kept to the confines of copyright law but

also not trumped by other copyright agreements or components of other

entirely separate legal systems.  In short, while GPLv2~\S\S0--3 are the parts

of the license that defend the freedoms of users and programmers,

GPLv2~\S\S4--7 are the parts of the license that keep the playing field clear

so that \S\S~0--3 can do their jobs.

\section{GPLv2~\S4: Termination on Violation}

\label{GPLv2s4}

GPLv2~\S4 is GPLv2's termination clause.  Upon first examination, it seems

strange that a license with the goal of defending users' and programmers'

freedoms for perpetuity in an irrevocable way would have such a clause.

However, upon further examination, the difference between irrevocability

The GPL is irrevocable in the sense that once a copyright holder grants

rights for someone to copy, modify and redistribute the software under terms

of the GPL, they cannot later revoke that grant.  Since the GPL has no

provision allowing the copyright holder to take such a prerogative, the

license is granted as long as the copyright remains in effect.\footnote{In

  the USA, due to unfortunate legislation, the length of copyright is nearly

  perpetual, even though the Constitution forbids perpetual copyright.} The

copyright holders have the right to relicense the same work under different

licenses (see Section~\ref{Proprietary Relicensing} of this tutorial), or to

stop distributing the GPLv2'd version (assuming GPLv2~\S3(b) was never used),

but they may not revoke the rights under GPLv2 already granted.

In fact, when an entity loses their right to copy, modify and distribute

GPL'd software, it is because of their \emph{own actions}, not that of the

copyright holder.  The copyright holder does not decide when GPLv2~\S4

termination occurs (if ever); rather, the actions of the licensee determine

that.

Under copyright law, the GPL has granted various rights and freedoms to

the licensee to perform specific types of copying, modification, and

redistribution.  By default, all other types of copying, modification, and

redistribution are prohibited.  GPLv2~\S4 says that if you undertake any of

those other types (e.g., redistributing binary-only in violation of GPLv2~\S3),

then all rights under the license --- even those otherwise permitted for

those who have not violated --- terminate automatically.

GPLv2~\S4 makes GPLv2 enforceable.  If licensees fail to adhere to the

license, then they are stuck without any permission under to engage in

activities covered by copyright law.  They must completely cease and desist

from all copying, modification and distribution of the GPL'd software.

At that point, violating licensees must gain the forgiveness of the copyright

holders to have their rights restored.  Alternatively, the violators could

negotiate another agreement, separate from GPL, with the copyright

holder.  Both are common practice, although

\tutorialpartsplit{as discussed in \textit{A Practical Guide to GPL

    Compliance}, there are }{Chapter~\ref{compliance-understanding-whos-enforcing}

  explains further} key differences between these two very different uses of GPL.

\section{GPLv2~\S5: Acceptance, Copyright Style}

\label{GPLv2s5}

GPLv2~\S5 brings us to perhaps the most fundamental misconception and common

confusion about GPLv2\@. Because of the prevalence of proprietary software,

most users, programmers, and lawyers alike tend to be more familiar with

EULAs. EULAs are believed by their authors to be contracts, requiring

formal agreement between the licensee and the software distributor to be

valid. This has led to mechanisms like ``shrink-wrap'' and ``click-wrap''

as mechanisms to perform acceptance ceremonies with EULAs.

The GPL does not need contract law to ``transfer rights.''  Usually, no rights

are transferred between parties.  By contrast, the GPL is primarily a permission

slip to undertake activities that would otherwise have been prohibited

by copyright law.  As such, GPL needs no acceptance ceremony; the

licensee is not even required to accept the license.

However, without the GPL, the activities of copying, modifying and

distributing the software would have otherwise been prohibited.  So, the

GPL says that you only accepted the license by undertaking activities that

you would have otherwise been prohibited without your license under GPL\@.

This is a certainly subtle point, and requires a mindset quite different

from the contractual approach taken by EULA authors.

An interesting side benefit to GPLv2~\S5 is that the bulk of users of Free

Software are not required to accept the license.  Undertaking fair and

unregulated use of the work, for example, does not bind you to the GPL,

since you are not engaging in activity that is otherwise controlled by

copyright law.  Only when you engage in those activities that might have an

impact on the freedom of others does license acceptance occur, and the

terms begin to bind you to fair and equitable sharing of the software.  In

other words, the GPL only kicks in when it needs to for the sake of

freedom.

While GPL is by default a copyright license, it is certainly still possible

to consider GPL as a contract as well.  For example, some distributors chose

to ``wrap'' their software in an acceptance ceremony to the GPL, and nothing in

the GPL prohibits that use.  Furthermore, the ruling in \textit{Jacobsen

  v. Katzer, 535 F.3d 1373, 1380 (Fed.Cir.2008)} indicates that \textbf{both}

copyright and contractual remedies may be sought by a copyright holder

seeking to enforce a license designed to uphold software freedom.

% FIXME-LATER: Write this

%\section{Using GPL Both as a Contract and Copyright License}

\section{GPLv2~\S6: GPL, My One and Only}

\label{GPLv2s6}

A point that was glossed over in Section~\ref{GPLv2s4}'s discussion of GPLv2~\S4

was the irrevocable nature of the GPL\@. The GPLv2 is indeed irrevocable,

and it is made so formally by GPLv2~\S6.

The first sentence in GPLv2~\S6 ensures that as software propagates down the

distribution chain, that each licensor can pass along the license to each

new licensee.  Under GPLv2~\S6, the act of distributing automatically grants a

license from the original licensor to the next recipient.  This creates a

chain of grants that ensure that everyone in the distribution has rights

under the GPLv2\@.  In a mathematical sense, this bounds the bottom ---

making sure that future licensees get no fewer rights than the licensee before.

The second sentence of GPLv2~\S6 does the opposite; it bounds from the top.  It

prohibits any licensor along the distribution chain from placing

additional restrictions on the user.  In other words, no additional

requirements may trump the rights and freedoms given by GPLv2\@.

The final sentence of GPLv2~\S6 makes it abundantly clear that no individual

entity in the distribution chain is responsible for the compliance of any

other.  This is particularly important for noncommercial users who have

passed along a source offer under GPLv2~\S3(c), as they cannot be assured that

the issuer of the offer will honor their GPLv2~\S3 obligations.

In short, GPLv2~\S6 says that your license for the software is your one and

only copyright license allowing you to copy, modify and distribute the

software.

GPLv2~\S6 is GPLv2's ``automatic downstream licensing''

provision\footnote{This section was substantially expanded for clarity and

  detail in \hyperref[GPLv3s10]{GPLv3~\S10}.}.  Each time you

redistribute a GPL'd program, the recipient automatically receives a license

from each original licensor to copy, distribute or modify the program subject

to the conditions of the license.  The redistributor need not take any

to ensure the downstream recipient's acceptance of the license terms.

This places every copyright holder in the chain of descent of the code

in legal privity, or direct relationship, with every downstream

redistributor.  Two legal effects follow.  First, downstream parties

who remain in compliance have valid permissions for all actions

(including modification and redistribution) even if their immediate upstream

supplier of the software has been terminated for license

violation\footnote{\label{German-reinstatement-footnote} While this is legally true, as a practical matter, a

  failure of ``complete, corresponding source'' (CCS) provisioning by an

  upstream could make it effectively impossible for a downstream party to

  engage in a commercial redistribution pursuant to

  \hyperref[GPLv2s3]{GPLv2~\S3(a--b)}.  (\S~\ref{upstream} in the Compliance

  Guide portion of this tutorial discussed related details.)}.

Downstream's

licensed rights are not dependent on compliance of their upstream, because

their licenses issue directly from the copyright holder.  Second, automatic

termination cannot be cured by obtaining additional copies from an alternate

supplier: the license permissions emanate only from the original licensors,

and if they have automatically terminated permission, no act by any

intermediate license holder can restore those terminated

rights\footnote{While nearly all attorneys and copyleft theorists are in

  agreement on this point, German copyleft legal expert

  \href{http://www.jbb.de/en/attorneys/till-jaeger/}{Till Jaeger}

  vehemently disagrees.  Jaeger's position is as follows: under German

  copyright law, a new copy of GPL'd software is a ``fresh'' license under

  GPL, and if compliance continues from that point further, the violator's

  permissions under copyright law are automatically restored, notwithstanding

  the strict termination provision in \hyperref[GPLv2s4]{GPLv2~\S4}.

  However, in

  practice, this issue is only salient with regard to \hyperref[Proprietary

    Relicensing]{proprietary relicensing} business models, since other copyright

  holders typically formally restore distributions rights once the only

  remaining compliance issue is ``you lost copyright permission due to

  GPLv2~\S4''.  Therefore, the heated debates, which have raged between

  Jaeger and almost everyone else in the copyleft community for nearly a

  decade, regard an almost moot and wholly esoteric legal detail.}.

\section{GPLv2 Irrevocability}

There are two legal theories why a contributor cannot terminate their license

grant. First is an argument that the text of the GPL prevents it; second is

that a contributor would be estopped from succeeding on an infringement claim

for continued use of the code even if it wasn't removed.

\subsection{The text of the GPLv2}

The GPLv2 have several provisions that, when taken together, can be construed

as an irrevocable license from each contributor. First, the GPLv2 says ``by

\emph{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'' (GPLv2\S5, emphasis added).  A contributor by definition is modifying

the code and therefore has agreed to all the terms in the GPLv2, which

includes the web of mechanisms in the GPLv2 that ensure the code can be used

by all.

More specifically, the downstream license grant says ``the recipient

automatically receives a license from the original licensor to copy,

distribute or modify the Program subject to these terms and conditions.''

(GPLv2\S6). So in this step, the contributor has granted a license to the

downstream, on the condition that the downstream complies with the license

terms.

That license granted to downstream is irrevocable, again provided that the

downstream user complies with the license terms: ``[P]arties 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''

(GPLv2\S4).

Thus, anyone downstream of the contributor (which is anyone using the

contributor's code), has an irrevocable license from the contributor. A

contributor may claim to revoke their grant, and subsequently sue for

copyright infringement, but a court would likely find the revocation was

ineffective and the downstream user had a valid license defense to a claim of

infringement.

Nevertheless, for purposes of argument, we will assume that for some

reason the GPLv2 is not enforceable against the contributor\footnote{For

  example, the argument has been made that there may be a failure of

  consideration on the part of the contributor. While \textit{Jacobsen

    v. Katzer}, 535 F.3d 1373 (Fed. Cir. 2008) is accepted as holding that

  there is consideration received by the contributor in a FOSS license, the

  posture of the case was one where the contributor advocated for the theory,

  not against it. The author is not aware of any other decisions that have analyzed

  the question in any depth, so it perhaps could be challenged in the right

  factual situation.}, or that the irrevocable license can be

revoked\footnote{A contract without a definable duration can be terminated on

  reasonable notice. \textit{Great W. Distillery Prod. v. John A. Wathen Distillery

  Co.}, 10 Cal. 2d 442, 447, 74 P.2d 745, 747 (1937). The term nevertheless

  can be a term of indefinite length where its continuing effect is tied to

  the conduct of the parties. \emph{Id}.}. In that case, the application of

promissory estoppel will likely mean that the contributor still cannot

enforce their copyright against downstream users.

\subsection{Promissory estoppel}

``Promissory estoppel'' is a legal theory that says, under some

circumstances, a promise is enforceable against the promisee even after the

promisee tries to renege on the promise. The test for how and when promissory

estoppel applies differs from state to state, but generally where there is a

``promise which the promisor should reasonably expect to induce action or

forbearance on the part of the promisee or a third person and which does

induce such action or forbearance is binding if injustice can be avoided only

by enforcement of the promise.''\footnote{\textit{Kajima/Ray Wilson v. Los Angeles

Cty. Metro. Transp. Auth.}, 23 Cal. 4th 305, 310, 1 P.3d 63, 66 (2000), \emph{citing}

Restatement (Second) of Contracts \S 90(1) (1979).} Breaking it down, it is:

\begin{enumerate}

\item where there is a clear and definite promise;

\item where the promisor has a reasonable expectation that the offer will

  induce action or forbearance on the part of the promisee;

\item which does induce actual and reasonable action or forbearance by the promisee; and

\item which causes a detriment which can only be avoided by the enforcement

  of the promise.

\end{enumerate}

In this case, the promisor is the contributor. This should be an easy

standard to meet in any widely used software.

\begin{enumerate}

\item The promise is contained in the GPL, which is a promise that one can

  continue to use the licensed software as long as the terms of the license

  are met.

\item A contributor knows that there is a broad user base and users consume

  the software relying on the grant in the GPL as assuring their continued

  ability to use the software (one might even say it is the \textit{sine qua

    non} of the intent of the GPL).

\item Users do, in fact, rely on the promises in the GPL, as they ingest the software

  and base their businesses on their continued ability to use the software.

\item Whether the user will suffer detriment is case-specific, but using

  Linux, a software program that is often fundamental to the operation of a