The copyright holders of Gmsh give you permission to combine Gmsh
  with code included in the standard release of Netgen (from Joachim
  Sch"oberl), METIS (from George Karypis at the University of
  Minnesota), OpenCASCADE (from Open CASCADE S.A.S) and ParaView
  (from Kitware, Inc.) under their respective licenses. You may copy
  and distribute such a system following the terms of the GNU GPL for
  Gmsh and the licenses of the other code concerned, provided that
  you include the source code of that other code when and as the GNU
  GPL requires distribution of source code.

  Note that people who make modified versions of Gmsh are not
  obligated to grant this special exception for their modified
  versions; it is their choice whether to do so. The GNU General
  Public License gives permission to release a modified version
  without this exception; this exception also makes it possible to
  release a modified version which carries forward this exception.
