Additional IP Rights Grant (Patents)
  
  "This implementation" means the copyrightable works distributed by
  Google as part of the Go project.
  
  Google hereby grants to You a perpetual, worldwide, non-exclusive,
  no-charge, royalty-free, irrevocable (except as stated in this section)
  patent license to make, have made, use, offer to sell, sell, import,
  transfer and otherwise run, modify and propagate the contents of this
  implementation of Go, where such license applies only to those patent
  claims, both currently owned or controlled by Google and acquired in
  the future, licensable by Google that are necessarily infringed by this
  implementation of Go.  This grant does not include claims that would be
  infringed only as a consequence of further modification of this
  implementation.  If you or your agent or exclusive licensee institute or
  order or agree to the institution of patent litigation against any
  entity (including a cross-claim or counterclaim in a lawsuit) alleging
  that this implementation of Go or any code incorporated within this
  implementation of Go constitutes direct or contributory patent
  infringement, or inducement of patent infringement, then any patent
  rights granted to you under this License for this implementation of Go
  shall terminate as of the date such litigation is filed.