[1] Indian Inst Technol, Dept Comp Sci & Engn, Kanpur 208016, Uttar Pradesh, India
[2] Indian Inst Technol, Dept Comp Sci & Engn, Kharagpur 721302, W Bengal, India
[3] Univ Hamburg, Dept Comp Sci, D-20148 Hamburg, Germany
[4] Fordham Univ, Dept Comp & Informat Sci, New York, NY 10458 USA