[1] IIT Kanpur, Dept Math & Stat, Kanpur 208016, Uttar Pradesh, India
[2] Peoples Friendship Univ Russia RUDN Univ, 6 Miklukho Maklaya St, Moscow 117198, Russia
[3] Univ Lyon 1, Inst Camille Jordan, CNRS, UMR 5208, F-69622 Villeurbanne, France
[4] INRIA Lyon La Doua, INRIA Team Dracula, F-69603 Villeurbanne, France