The copyright license of the POWHEG software is the GNU General Public License (GPL) version 2. Please read the MCNET GUIDELINES (in the MCNET-GUIDELINES file) for details. You are required to adhere to the guidelines when using this code. As far as the POWHEG BOX is concerned, the guideline 1.1) in the MCNET GUIDELINES can be interpreted more loosely. If you add a process to the POWHEG BOX, you should try as much as possible to do it in such a way that your work can be integrated in the full POWHEG BOX software. In particular, you should try to avoid performing changes to the POWHEG BOX common software that break other implemented processes. If you need to modify common files, contact us, since we would like to keep a single development branch of the common code.