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\begin{center}

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{\Large

{\sc Detailed Study and Analysis of GPL and LGPL  } \\

\vspace{.7in}

Sponsored by the Free Software Foundation \\

\vspace{.3in}

Columbia Law School, New York, NY, USA \\

\vspace{.1in}

}

\vspace{.7in}

{\large

Bradley M. Kuhn

Executive Director

Free Software Foundation

}

\vspace{.3in}

{\large

Daniel Ravicher

Senior Counsel 

Free Software Foundation

}

\end{center}

learned the following:

\begin{itemize}

  \item the freedom-defending purpose of each term of the GNU GPL.

  \item the redistribution options under the GPL.

  \item the obligations when modifying GPL'd software.

  \item how to build a plan for proper and successful compliance with the GPL.

  \item the business advantages that the GPL provides.

  \item the most common business models used in conjunction with the GPL.

  \item how existing GPL'd software can be used in existing enterprises.

  \item the basics of the LGPL and how it differs from GPL.

  \item how best to understand the complexities regarding derivative

        works of software.

\end{itemize}

\end{abstract}

\tableofcontents

\pagebreak

\pagenumbering{arabic}

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

\chapter{What Is Free Software?}

Consideration of the GNU General Public License (herein, abbreviated as

\defn{GNU GPL} or just \defn{GPL}) must begin by first considering the broader

world of Free Software.  The GPL was not created from a void, rather,

it was created to embody and defend a set of principles that were set

forth at the founding of the GNU project and the Free Software Foundation

(FSF)---the organization that upholds, defends and promotes the philosophy

of software freedom.  A prerequisite for understanding the GPL and its

terms and conditions is a basic understanding of the principles behind it.

The GPL is unlike almost all other software licenses in that it is

designed to defend and uphold these principles.

\section{The Free Software Definition}

\label{Free Software Definition}

incentives do not depend upon perfect control over the products created.

Like jazz, or novels, or architecture, the law gets built upon the work

that went before. This adding and changing is what creativity always is.

And a free society is one that assures that its most important resources

remain free in just this sense.\footnote{This quotation is Copyright

  \copyright{} 2002, Lawrence Lessig.  It is licensed under the terms of

  \href{http://creativecommons.org/licenses/by/1.0/}{the ``Attribution

    License'', version 1.0} or any later version as published by Creative

  Commons.}

\end{quotation}

In essence, lawyers are paid to service the shared commons of legal

infrastructure.  Few citizens defend themselves in court or write their

own briefs (even though they are legally permitted to do so) because

everyone would prefer to have an expert do that job.

The Free Software economy is a market that is ripe for experts.  It

functions similarly to other well established professional fields like the

law.  The GPL, in turn, serves as the legal scaffolding that permits the

creation of this vibrant commercial and non-commercial Free Software

economy.

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

\chapter{Running Software And Verbatim Copying}

This chapter begins the deep discussion of the details of the terms of

GPL\@.  In this chapter, we consider the first two sections: GPL \S\S

0--2.  These are the straightforward sections of the GPL that define the

simplest rights that the user receives.

\section{GPL \S 0: Freedom to Run}

\label{GPLs0}

\S 0, the opening section of GPL, sets forth that the work is governed by

copyright law.  It specifically points out that it is the ``copyright

holder'' who decides if a work is licensed under its terms, and explains

how the copyright holder might indicate this fact.

A bit more subtly, \S 0 makes an inference that copyright law is the only

system under which it is governed.  Specifically, it states:

\begin{quote}

Activities other than copying, distribution and modification are not

covered by this License; they are outside its scope.

\end{quote}

In essence, the license governs \emph{only} those activities and all other

activities are unrestricted, provided that no other agreements trump GPL

(which they cannot; see Sections~\ref{GPLs6} and~\ref{GPLs7}).  This is

very important, because the Free Software community heavily supports

not attempting to cover them.  Furthermore, the GPL ensures the freedom

to run specifically by stating the following:

\begin{quote}

The act of running the Program is not restricted

\end{quote}

Thus, users are explicitly given the freedom to run by \S 0.

\medskip

The bulk of \S 0 not yet discussed gives definitions for other terms used

throughout.  The only one worth discussing in detail is ``work based on

the Program''.  The reason this definition is particularly interesting is

not for the definition itself, which is rather straightforward, but the

because it clears up a common misconception about the GPL\@.

The GPL is often mistakenly criticized because it fails to give a

definition of ``derivative work''.  In fact, it would be incorrect and

problematic if the GPL attempted to define this.  A copyright license, in

fact, has no control over what may or may not be a derivative work.  This

matter is left up to copyright law, not the licenses that utilize it.

It is certainly true that copyright law as a whole does not propose clear

and straightforward guidelines for what is and is not a derivative

software work under copyright law.  However, no copyright license --- not

opinions must give us guidance to decide the border cases.

\section{GPL \S 1: Verbatim Copying}

\label{GPLs1}

GPL \S 1 covers the matter of redistributing the source code of a program

exactly as it was received.  This section is quite straightforward.

However, there are a few details worth noting here.

The phrase ``in any medium'' is important.  This, for example, gives the

freedom to publish a book that is the printed copy of the program's source

code.  It also allows for changes in the medium of distribution.  Some

vendors may ship Free Software on a CD, but others may place it right on

the hard drive of a pre-installed computer.  Any such redistribution media

is allowed.

Preservation of copyright notice and license notifications are mentioned

specifically in \S 1.  These are in some ways the most important part of

the redistribution, which is why they are mentioned by name.  The GPL

always strives to make it abundantly clear to anyone who receives the

software what its license is.  The goal is to make sure users know their

rights and freedoms under GPL and to leave no reason that someone would be

surprised that the software she got was licensed under GPL\@.  Thus

throughout the GPL, there are specific reference to the importance of

Circuit. Some Circuits, including the Ninth Circuit and the First Circuit,

have either adopted narrower versions of the AFC test or have expressly

rejected the AFC test in favor of a narrower standard. Further, several

other Circuits have yet to adopt any definition of derivative work for

software.

As an introductory matter, it is important to note that literal copying of

a significant portion of source code is not always sufficient to establish

that a second work is a derivative work of an original

program. Conversely, a second work can be a derivative work of an original

program even though absolutely no copying of the literal source code of

the original program has been made. This is the case because copyright

protection does not always extend to all portions of a program’s code,

while, at the same time, it can extend beyond the literal code of a

program to its non-literal aspects, such as its architecture, structure,

sequence, organization, operational modules, and computer-user interface.

\section{The Copyright Act}

The copyright act is of little, if any, help in determining the definition

of a derivative work of software. However, the applicable provisions do

provide some, albeit quite cursory, guidance. Section 101 of the Copyright

Act sets forth the following definitions:

A ``computer program'' is a set of statements or instructions to be used

directly or indirectly in a computer in order to bring about a certain

result.

A ``derivative work'' is a work based upon one or more preexisting works,

such as a translation, musical arrangement, dramatization,

fictionalization, motion picture version, sound recording, art

reproduction, abridgment, condensation, or any other form in which a work

may be recast, transformed, or adapted. A work consisting of editorial

revisions, annotations, elaborations, or other modifications which, as a

whole, represent an original work of authorship, is a ``derivative work''.

These are the only provisions in the Copyright Act relevant to the

determination of what constitutes a derivative work of a computer

program. Another provision of the Copyright Act that is also relevant to

the definition of derivative work is \S 102(b), which reads as follows:

\begin{quotation}

In no case does copyright protection for an original work of authorship

extend to any idea, procedure, process, system, method of operation,

concept, principle, or discovery, regardless of the form in which it is

described, explained, illustrated, or embodied in such work.

\end{quotation}

Therefore, before a court can ask whether one program is a derivative work

of another program, it must be careful not to extend copyright protection

to any ideas, procedures, processes, systems, methods of operation,

concepts, principles, or discoveries contained in the original program. It

is the implementation of this requirement to ``strip out'' unprotectable

elements that serves as the most frequent issue over which courts

disagree.

\section{Abstraction, Filtration, Comparison Test}

As mentioned above, the AFC test for determining whether a computer

in the public domain or required by functional demands on the

program. With respect to the handful of parameter lists and macros that

did qualify for copyright protection, after performing the comparison step

of the AFC test, it was reasonable for the district court to conclude that

they did not warrant a finding of infringement given their relative minor

contribution to the program as a whole.  Likewise, the similarity between

the organizational charts of the two programs was not substantial enough

to support a finding of infringement because they were too simple and

obvious to contain any original expression.

Perhaps not surprisingly, there have been few cases involving a highly

detailed software derivative work analysis.  Most often, cases involve

clearer basis for decision, including frequent bad faith on the part of

the defendant or over aggressiveness on the part of the plaintiff.

However, no cases involving free software licensing have ever gone to

court.  As free software becomes an ever increasingly important part of

the economy, it remains to be seen whether or not battle lines will be

drawn over whether particular programs infringe the rights of free

software developers or whether the entire community, including industry,

adopts norms avoiding such risk.

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

\chapter{Modified Source and Binary Distribution}

In this chapter, we discuss the two core sections that define the rights

and obligations for those who modify, improve, and/or redistribute GPL'd

software.  These sections, \SS 2--3, define the central core rights and

requirements of GPL\@.

\section{GPL \S 2: Share and Share Alike}

For many, this is where the ``magic'' happens that defends software

freedom along the distribution chain.  \S 2 is the only place in the GPL

that governs the modification controls of copyright law.  If someone

modifies a GPL'd program, she is bound in the making those changes by \S

2.  The goal here is to ensure that the body of GPL'd software, as it

continues and develops, remains Free as in freedom.

To achieve that goal, \S 2 first sets forth that the rights of

redistribution of modified versions are the same as those for verbatim

copying, as presented in \S 1.  Therefore, the details of charging,

keeping copyright notices intact, and other \S 1 provisions are in tact

here as well.  However, there are three additional requirements.

The first (\S 2(a)) requires that modified files carry ``prominent

notices'' explaining what changes were made and the date of such changes.

The goal here is not to put forward some specific way of marking changes,

is distributed amongst 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 GPL ensures that the community mutually

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

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

not mean that any patents held by a distributor of GPL'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 GPL by the patent

  holder, and

\item any party that does not comply with the GPL

with respect to the licensed software.

\end{enumerate}

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

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

also licenses a web browsing software program under the GPL, then it

cannot assert the patent against any party that takes a license to its

program under the GPL.  However, if a party uses that program without

infringement claims against the non-GPL-compliant party, but also

infringement of the patent, because the implied patent license only

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

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

implied licenses to Company \compA's patent.

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

proprietary value in patents to competitors through the GPL implied patent

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

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

redistributed Company A's advanced web browser under the GPL.  If Company

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

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

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

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

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}

\section{GPL \S 4: Termination on Violation}

\label{GPLs4}

\S 4 is GPL's termination clause.  Upon first examination, it seems

strange for a license that has 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

and this termination clause becomes clear.

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 holder has the right to relicense the same

work under different licenses (see Section~\ref{Proprietary Relicensing}

of this tutorial), or to stop distributing the GPL'd version (assuming \S

3(b) was never used), but the she may not revoke the rights under GPL

already granted.

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

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.  \S 4 says that if you undertake any of

those other types (e.g., redistributing binary-only in violation of \S 3),

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

those who have not violated --- terminate automatically.

\S 4 gives GPL teeth.  If licensees fail to adhere to the license, then

they are stuck.  They must to completely cease and desist from all

copying, modification and distribution of that GPL'd software.

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

copyright holder to have their rights restored.  Alternatively, they could

negotiate another agreement, separate from GPL, with the copyright

holder.  Both are common practice.

At FSF, it is part of the mission to spread software freedom.  When FSF

enforces GPL, the goal is to bring the violator back into compliance as

quickly as possible, and redress the damage caused by the violation.

That is FSF's steadfast position in a violation negotiation --- comply

with the license and respect freedom.

However, other entities who do not share the full ethos of software

\section{GPL \S 5: Acceptance, Copyright Style}

\label{GPLs5}

\S 5 brings us to perhaps the most fundamental misconception and common

confusion about GPL\@.  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''.  No rights are

transfered between parties.  By contrast, the GPL is permission slip to

undertake activities that would otherwise been prohibited by copyright law.

As such, it 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.

Again, some have argued the GPL is unenforceable in some jurisdictions

because its limitation of liability is impermissibly broad.  However, \S

12, just like its sister, \S 11, contains a jurisdictional savings

provision, which states that it is to be interpreted only as broadly as

allowed by applicable law.  As stated above, such a provision ensures that

both \S 12, and the entire GPL, is enforceable in any jurisdiction,

regardless of any particular law regarding the permissibility of limiting

liability.

So ends the terms and conditions of the GNU General Public License.

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

\chapter{The Lesser GPL}

As we have seen in our consideration of the GPL, its text is specifically

designed to cover all possible derivative works under copyright law.  Our

goal in designing GPL was to make sure that any derivative work of GPL'd

software was itself released under GPL when distributed.  Reaching as far

as copyright law will allow is the most direct way to reach that goal.

However, while the strategic goal is to bring as much Free Software into

the world as possible, particular tactical situations of software freedom

dictate different means.  Extending the copyleft effect as far as

License (``GNU LGPL'') was designed as a solution for such situations.

\section{The First LGPL'd Program}

The first example that FSF encountered where such altered tactics were

needed was when work began on the GNU C Library.  The GNU C Library would

construct a program that will run with ease on a Unix-like operating

make use of the C Library.

By the time work began on the GNU implementation of the C Library, there

were already many C libraries in existence from a variety of vendors.

Every proprietary Unix vendor had one, and many third parties produced

smaller versions for special purpose use.  However, our goal was to create

a C library that would provide equivalent functionality to these other C

Unlike existing GNU application software, however, the licensing

implications of releasing the GNU C Library (``glibc'') under GPL were

somewhat different.  Applications released under GPL would never

themselves become part of proprietary software.  However, if glibc were

released under GPL, it would require that any application distributed for

Since all applications on a Unix-like system depend on the C library, it

means that they must link with that library to function on the system.  In

other words, all applications running on a Unix-like system must be

combined with the C library to form a new whole derivative work that is

composed of the original application and the C library.  Thus, if glibc

were GPL'd, each and every application distributed for use on GNU/Linux

would also need to be GPL'd, since to even function, such applications

would need to be combined into larger derivative works by linking with

glibc.

At first glance, such an outcome seems like a windfall for Free Software

advocates, since it stops all proprietary software development on

GNU/Linux systems.  However, the outcome is a bit more subtle.  In a world

where many C Libraries already exist, many of which could easily be ported

to GNU/Linux, a GPL'd glibc would be unlikely to succeed.  Proprietary

glibc, but the most popular proprietary one.

Meanwhile, the actual goal of releasing glibc under GPL --- to ensure no

proprietary applications on GNU/Linux --- would be unattainable in this

scenario.  Furthermore, users of those proprietary applications would also

inevitable.  Since there were so many C libraries already in existence, a

new one under GPL would not stop that tide.  However, if the new C library

were released under a license that (a) permitted proprietary applications

to link with it, but (b) made sure that the library itself remained Free,

an ancillary goal could be met.  Users of proprietary applications, while

they would not have the freedom to copy, share, modify and redistribute

the application itself, would have the freedom to do so with respect to

the C library.

There was no way the license of glibc could stop or even slow the creation

of proprietary applications on GNU/Linux.  However, loosening the

Of course, many people who use the LGPL today are not thinking in these

\section{What's the Same?}

Much of the text of the LGPL is identical to the GPL\@.  As we begin our

discussion of the LGPL, we will first eliminate the sections that are

First, \S 1 of LGPL, the rules for verbatim copying of source, are

equivalent to those in GPL's \S 1.

Second, \S 8 of LGPL is equivalent \S 4 of GPL\@.  In both licenses, this

section handles termination in precisely the same manner.

\S 9 in LGPL is equivalent to \S 5 in GPL\@.  Both sections assert that

the license is a copyright license, and handle the acceptance of those

copyright terms.

LGPL's \S 10 is equivalent to GPL's \S 6.  They both protect the

distribution system of Free Software under these licenses, to ensure that

up, down, and throughout the distribution chain, each recipient of the

software receives identical rights under the license and no other

restrictions are imposed.

LGPL's \S 11 is GPL's \S 7.  As discussed, it is used to ensure that

other claims and legal realities, such as patent licenses and court

judgments, do not trump the rights and permissions granted by these

licenses, and requires that distribution be halted if such a trump is

known to exist.

LGPL's \S 12 adds the same features as GPL's \S 8.  These sections are

\begin{itemize}

\item A new copyright holder creates a separate and independent work,

  \worki{}, that makes interface calls (e.g., function calls) to the

  LGPL'd work, called \workl{}, whose copyright is held by some other

  party.  Note that since \worki{} and \workl{} are separate and

  independent works, there is no copyright obligation on this new copyright

  holder with regard to the licensing of \worki{}, at least with regard to

  the source code.

\item The new copyright holder, for her software to be useful, realizes

  that it cannot run without combining \worki{} and \workl{}.

  Specifically, when she creates a running binary program, that running

  binary must be a derivative work, called \lplusi{}, that the user can

  run.

\item Since \lplusi{} is a derivative work of both \worki{} and \workl{},

  the license of \workl{} (the LGPL) can put restrictions on the license

  of \lplusi{}.  In fact, this is what LGPL does.

\end{itemize}

We will talk about the specific restrictions LGPL places on ``works that

In addition, the only reason that LGPL has any control over the licensing

of a ``work that uses the library'' is for the same reason that GPL has

some say over separate and independent works.  Namely, such controls exist

because the {\em binary combination\/} (\lplusi{}) that must be created to

make the separate work (\worki{}) at all useful is a derivative work of

the LGPL'd software (\workl{}).

Thus, a two-question test that will help indicate if a particular work is

a ``work that uses the library'' under LGPL is as follows:

\begin{enumerate}

\item Is the source code of the new copyrighted work, \worki{}, a

  completely independent work that stands by itself, and includes no

  source code from \workl{}?

\item When the source code is compiled, does it create a derivative work

  by combining with \workl{}, either by static (compile-time) or dynamic

  (runtime) linking, to create a new binary work, \lplusi{}?

\end{enumerate}

If the answers to both questions are ``yes'', then \worki{} is most likely

a ``work that uses the library''.  If the answer to the first question

At times, though, we have seen cases where it almost appeared as such ---

that a derivative work appeared in some ways to be a work that used the

library and in other ways a work based on the library.  We overcame this

problem by dividing the work into smaller subunits.  It was soon

discovered that what we actually had were three distinct components -- the

original LGPL'd work, a specific set of works that used that library, and

a specific set of works that were based on the library.  Once such

distinctions are established, the licensing for each component can be

considered independently and the LGPL applied to each work as prescribed.

\section{Subtleties in Works that Use the Library}

In our discussion of the definition of ``works that use the library'', we

left out a few more complex details that relate to lower level programming

details.  The forth paragraph of LGPL's \S 5 covers these complexities,

and it has been a source of great confusion.  Part of the confusion comes

because a deep understanding of how compiler programs work is nearly

mandatory to understand the subtle nature of what \S 5, \P 4 seeks to

cover.  It helps some to note that this is a border case that we cover in

the license only so that when such a border case is hit, the implications

of using LGPL continue in the expected way.

To understand this subtle point, we must recall the way that a compiler

As we have discussed, the assembly of modules can happen at compile-time

or at runtime.  Legally, there is no distinction between the two --- both

create a derivative work by copying and combining portions of one work and

mixing them with another.  However, under LGPL, there is a case in the

compilation process where the legal implications are different.

Specifically, while we know that a ``work that uses the library'' is one

whose final binary is a derivative work, but whose source is not, there

are cases where the object code --- that intermediate step between source

and final binary --- is a derivative work created by copying verbatim code

from the LGPL'd software.

For efficiency, when a compiler turns source code into object code, it

sometimes places literal portions of the copyrighted library code into the

object code for an otherwise separate independent work.  In the normal

scenario, the derivative would not be created until final assembly and

linking of the executable occurred.  However, when the compiler does this

efficiency optimization, at the intermediate object code step, a

derivative work is created.

LGPL's \S 5, \P 4 is designed to handle this specific case.  The intent of

the license is clearly that simply compiling software to ``make use'' of

the library does not in itself cause the compiled work to be a ``work

based on the library''.  However, since the compiler copies verbatim,

copyrighted portions of the library into the object code for the otherwise

separate and independent work, it would actually cause that object file a

``work based on the library''.  It is not FSF's intent that a mere

LGPL'd software.  This paragraph removes that restriction, allowing the

implications of the license to be the same regardless of the specific

mechanisms the compiler uses underneath to create the ``work that uses the

library''.

As it turns out, we have only once had anyone worry about this specific

idiosyncrasy, because that particular vendor wanted to ship object code

(rather than final binaries) to their customers and were worried about

this edge condition.  The intent of clarifying this edge condition is

primarily to quell the worries of software engineers who understand the

level of verbatim code copying that a compiler often does, and to help

them understand that the full implications of LGPL are the same regardless

of the details of the compilation progress.

\section{LGPL \S 6: Distributing Works that Use the Library}

Now that we have a established a good working definition of works that

``use'' and works that ``are based on'' the library, we will consider the

rules for distributing these two different works.

The rules for distributing ``works that use the library'' are covered in

\S 6 of LGPL\@.  \S 6 is much like GPL's \S 3, as it requires the release

of source when a binary version of the LGPL'd software is released.  Of

course, it only requires that source code for the library itself be made

available.  The work that ``uses'' the library need not be provided in

source form.  However, there are also conditions in LGPL \S 6 to make sure

that a user who wishes to modify or update the library can do so.

LGPL \S 6 lists five choices with regard to supplying library source and

\S 6(b) allows the distributor of a ``work that uses the library'' to

simply use a dynamically linked, shared library mechanism to link with the

library.  This is by far the easiest and most straightforward option for

distribution.  In this case, the executable of the work that uses the

library will contain only the ``stub code'' that is put in place by the

shared library mechanism, and at runtime the executable will combine with

the shared version of the library already resident on the user's computer.

If such a mechanism is used, it must allow the user to upgrade and

replace the library with interface-compatible versions and still be able

to use the ``work that use the library''.  However, all modern shared

library mechanisms function as such, and thus \S 6(b) is the simplest

option, since it does not even require that the distributor of the ``work

based on the library'' ship copies of the library itself.

\S 6(a) is the option to use when, for some reason, a shared library

mechanism cannot be used.  It requires that the source for the library be

included, in the typical GPL fashion, but it also has a requirement beyond

that.  The user must be able to exercise her freedom to modify the library

to its fullest extent, and that means recombining it with the ``work based

on the library''.  If the full binary is linked without a shared library

mechanism, the user must have available the object code for the ``worked

based on the library'', so that the user can relink the application and

build a new binary.

The remaining options in \S 6 are very similar to the other choices

\section{Distribution of Works Based on the Library}

\section{And the Rest}

The remaining variations between LGPL and GPL cover the following

conditions:

\begin{itemize}

\item allowing a licensing ``upgrade'' from LGPL to GPL\@ (in LGPL \S 3),