patent claims.

Finally, GPLv3's explicit patent license for contributors has an interesting

and useful side effect.  When a company with a large number of such claims

acquires the program's modifier, all claims held or thereafter acquired by

the purchaser are automatically licensed under this provision.  For example,

Microsoft's acquisition of Nokia resulted in the automatic licensing of all

Microsoft patent claims now or hereafter acquired which read on any

contributor version of any GPLv3 program ever modified by Nokia.

\subsection{Conveyors' Patent Licensing}

The remaining patent licensing in GPLv3 deals with patent licenses that are

granted by conveyance.  The licensing is not as complete or far reaching as

the contributor patent licenses discussed in the preceding section.

The term ``patent license,'' as used in GPLv3~\S11\P4--6, is not meant to be

confined to agreements formally identified or classified as patent licenses.

GPLv3~\S11\P3  makes this clear by defining ``patent

license,'' for purposes of the subsequent three paragraphs, as ``any express

agreement or commitment, however denominated, not to enforce a patent

(such as an express permission to practice a patent or covenant not to

sue for patent infringement)''

GPLv3~\S11\P5 is commonly called GPLv3's downstream shielding provision.  It

responds particularly to the problem of exclusive deals between patent

holders and distributors, which threaten to distort the free software

distribution system in a manner adverse to developers and users.  The

fundamental idea is to make a trade-off between assuring a patent license for

downstream and making  (possibly patent-encumbered) CCS publicly available.

Simply put, in nearly all cases in which the ``knowingly relying'' test is

met, the patent license will indeed not be sublicensable or generally

available to all on free terms.  If, on the other hand, the patent license is

generally available under terms consistent with the requirements of the GPL,

the distributor is automatically in compliance, because the patent license

has already been extended to all downstream recipients.  Finally, if the

patent license is sublicensable on GPL-consistent terms, the distributor may

choose to grant sublicenses to downstream recipients instead of causing the

CCS to be publicly available.  (In such a case, if the distributor is also a

contributor, it will already have granted a patent sublicense anyway, and so

it need not do anything further to comply with the third paragraph.)

Admittedly, public disclosure of CCS is not necessarily required by other

sections of the GPL, and the FSF in drafting GPLv3 did not necessarily wish

to impose a general requirement to make source code available to all, which

has never been a GPL condition.  However, many vendors who produce products