Tunisian Journal of Mathematics an international publication organized by the Tunisian Mathematical Society Editors-in-Chief Ahmed Abbes, France Ali Baklouti, Tunisia Hajer Bahouri, France Arnaud Beauville, France Bassam Fayad, France Benoit Fresse, France Dennis Gaitsgory, United States Emmanuel Hebey, France Mohamed Ali Jendoubi, Tunisia Sadok Kallel, France & UAE Minhyong Kim, UK & Korea Toshiyuki Kobayashi, Japan Yanyan Li, United States Nader Masmoudi, United States Haynes R. Miller, United States Nordine Mir, Qatar & France Detlef Müller, Germany Mohamed Sifi, Tunisia Daniel Tataru, United States Sundaram Thangavelu, India Saïd Zarati, Tunisia Editorial Board Published in electronic and print formats by mathematical sciences publishers in Berkeley msp.org/tunisjm The TJM editorial board invites mathematicians from all over the world to submit high-level research articles.