1. L.R.I.,BÂT.490; UNIVERSITY PARIS 11 SUD; ORSAY CEDEX FRANCE
2. ALFRÉD RÉNYI INSTITUTE OF MATHEMATICS; HUNGARIAN ACADEMY OF SCIENCES; BUDAPEST HUNGARY
3. DEPARTMENT OF MATHEMATICAL AND STATISTICAL SCIENCES; UNIVERSITY OF COLORADO DENVER; DENVER COLORADO
4. INTERNATIONAL COLLEGE OF ARTS AND SCIENCES; YOKOHAMA CITY UNIVERSITY; KANAZAWA-KU YOKOHAMA JAPAN
5. DEPARTMENT OF MATHEMATICAL INFORMATION SCIENCE; TOKYO UNIVERSITY OF SCIENCE; SHINJUKU-KU TOKYO JAPAN
6. DEPARTMENT OF MATHEMATICS; INDIAN INSTITUTE OF TECHNOLOGY MADRAS; CHENNAI INDIA
7. DEPARTMENT OF MATHEMATICS; DEPARTMENT OF COMPUTER SCIENCE; IOWA STATE UNIVERSITY; AMES IOWA