1. DEPARTMENT OF COMPUTATION; UNIVERSITY OF THE STATE OF RIO DE JANEIRO; RIO DE JANEIRO BRAZIL
2. COPPE-SYSTEMS ENGINEERING AND COMPUTER SCIENCE; FEDERAL UNIVERSITY OF RIO DE JANEIRO; RIO DE JANEIRO BRAZIL
3. DEPARTMENT OF COMBINATORICS & OPTIMIZATION; UNIVERSITY OF WATERLOO; WATERLOO CANADA
4. INSTITUTE OF MATHEMATICS; SLOVAK ACADEMY OF SCIENCES; BRATISLAVA SLOVAK REPUBLIC