GPLv2 and patents
The GNU General Public License, version 2 (aka GPLv2) contains some protections against software patents, namely a prohibition on adding patent royalties, a prohibition on imposing further restrictions, and statements that may reinforce the implicit patent grant.
Two parts of GPLv2 imply that the distributor gives the downstream recipients a patent licence. In section 6, GPLv2 says that the distributor grants a licence to carry out the four freedoms. In section 7, it says that distribution is banned if the distributor has patent obligations preventing the recipient from having the four freedoms. So, if the distributor does distribute, then there is an acknowledgement that the recipient is free to do everything described in the licence.
 Patent grant: section 6
6. Each time you redistribute the Program (or any work based on the Program), the recipient automatically receives a license from the original licensor to copy, distribute or modify the Program subject to these terms and conditions. You may not impose any further restrictions on the recipients' exercise of the rights granted herein. You are not responsible for enforcing compliance by third parties to this License.
 Prohibition on royalties: section 7
7. If, as a consequence of a court judgment or allegation of patent infringement or for any other reason (not limited to patent issues), conditions are imposed on you (whether by court order, agreement or otherwise) that contradict the conditions of this License, they do not excuse you from the conditions of this License. If you cannot distribute so as to satisfy simultaneously your obligations under this License and any other pertinent obligations, then as a consequence you may not distribute the Program at all. For example, if a patent license would not permit royalty-free redistribution of the Program by all those who receive copies directly or indirectly through you, then the only way you could satisfy both it and this License would be to refrain entirely from distribution of the Program.
If any portion of this section is held invalid or unenforceable under any particular circumstance, the balance of the section is intended to apply and the section as a whole is intended to apply in other circumstances.
It is not the purpose of this section to induce you to infringe any patents or other property right claims or to contest validity of any such claims; this section has the sole purpose of protecting the integrity of the free software distribution system, which is implemented by public license practices. Many people have made generous contributions to the wide range of software distributed through that system in reliance on consistent application of that system; it is up to the author/donor to decide if he or she is willing to distribute software through any other system and a licensee cannot impose that choice.
This section is intended to make thoroughly clear what is believed to be a consequence of the rest of this License.
 Related pages on en.swpat.org
- The text of GPL version 2
- FSF lawyer recommends express patent license for GPL, BSD, 5 Nov 2004, ZDNet on Dan Ravicher
- "Transcript of Richard Stallman at the 5th international GPLv3 conference; 21st November 2006". http://www.fsfe.org/projects/gplv3/tokyo-rms-transcript. "in the US, when that company distributes the software under the GPL, they're telling people "We have no objections if you do what the GPL says you can do" and so if they tried to sue those same people for patent infringement later, they would lose."
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