1. Faculty of Mathematics and Computer Science University of Science Ho Chi Minh City Vietnam
2. Vietnam National University Ho Chi Minh City Vietnam
3. Laboratoire de Mathématiques UMR 8628, Université Paris Sud Orsay France
4. Ceremade, CNRS, UMR 7534 Université Paris‐Dauphine, PSL Research University Paris France
5. LAMA Univ Gustave Eiffel, UPEM, Univ Paris Est Creteil, CNRS Marne‐la‐Vallée France