1. Faculty of Mathematics and Computer Science, University of Science, Vietnam National University Ho Chi Minh city, Vietnam
2. LAGA, Institut Galilée, CNRS, UMR 7539, Université Sorbonne Paris Nord, 93430, Villetaneuse, France
3. CEREMADE, CNRS, Université Paris-Dauphine, Université PSL, 75016 Paris, France