1. XLIM Research Institute, University of Limoges, CNRS UMR 7252, Limoges, France.
2. Taras Shevchenko National University of Kyiv, Kyiv, Ukraine.
3. Laboratoire Jacques-Louis Lions, Sorbonne Universités, UPMC Univ Paris 06, CNRS UMR 7598, Paris, France.