More detail on Irrevocability of GPLv2

This section, fit in just after the detailed discussion of GPLv2 Section 6,
explains in futher detail various arguments for why the GPLv2 is irrevocable.

comprehensive-gpl-guide.tex

@@ -100,7 +100,8 @@ and Guide
 
 {\parindent 0in
 \begin{tabbing}
-Copyright \= \copyright{} 2003--2005, 2008, 2014--2015 \hspace{1.mm} \=  \kill
+Copyright \= \copyright{} 2003--2005, 2008, 2014--2015, 2018 \hspace{1.mm} \=  \kill
+Copyright \> \copyright{} 2018 \>  Chestek Legal. \\
 Copyright \> \copyright{} 2003--2005, 2008, 2014--2015 \>  Bradley M. Kuhn. \\
 Copyright \> \copyright{} 2014--2015 \>  Anthony K. Sebro, Jr. \\
 Copyright \= \copyright{} 2014 \> Denver Gingerich. \\

gpl-lgpl.tex

@@ -2320,6 +2320,117 @@ rights\footnote{While nearly all attorneys and copyleft theorists are in
   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
+  business, as an example, the loss of its use would have a significantly
+  detrimental, perhaps even fatal, effect on the continued operation of the
+  business.
+
+\end{enumerate}
+
+\subsection{Conclusion}
+
+Whether as a matter of a straightforward contractual obligation, or as a
+matter of promissory estoppel, a contributor's attempt to revoke a copyright
+license grant and then enforce their copyright against a user is highly
+unlikely to succeed.
+
 \section{GPLv2~\S7: ``Give Software Liberty or Give It Death!''}
 \label{GPLv2s7}