O. Shahar, Dept. of Comput. Sci. & Appl. Math, Weizmann Inst. of Sci., Rehovot, Israel A. Faktor, Dept. of Comput. Sci. & Appl. Math, Weizmann Inst. of Sci., Rehovot, Israel M. Irani, Dept. of Comput. Sci. & Appl. Math, Weizmann Inst. of Sci., Rehovot, Israel
