licenses with express patent grants, in that the patent license

clause of many of those other Free  Software licenses are specifically 

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 derivative 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 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 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 software program under the GPLv2, then it

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

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

creation and use of derivative works of that GPL'ed program.  However, if a