7-Zip manual: 7-Zip Manual License.txt

  7-Zip source code
  License for use and distribution

  7-Zip Copyright (C) 1999-2016 Igor Pavlov.

  Licenses for files are:

    1) CPP/7zip/Compress/Rar* files:  GNU LGPL + unRAR restriction
    2) All other files:  GNU LGPL

  The GNU LGPL + unRAR restriction means that you must follow both 
  GNU LGPL rules and unRAR restriction rules.

  GNU LGPL information

    This library is free software; you can redistribute it and/or
    modify it under the terms of the GNU Lesser General Public
    License as published by the Free Software Foundation; either
    version 2.1 of the License, or (at your option) any later version.

    This library is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    Lesser General Public License for more details.

    You should have received a copy of the GNU Lesser General Public
    License along with this library; if not, write to the Free Software
    Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301

  unRAR restriction

    The decompression engine for RAR archives was developed using source 
    code of unRAR program.
    All copyrights to original unRAR code are owned by Alexander Roshal.

    The license for original unRAR code has the following restriction:

    The unRAR sources cannot be used to re-create the RAR compression algorithm, 
    which is proprietary. Distribution of modified unRAR sources in separate form 
    or as a part of other software is permitted, provided that it is clearly
    stated in the documentation and source comments that the code may
    not be used to develop a RAR (WinRAR) compatible archiver.

  Igor Pavlov

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