(1) Department of Statistics, Korea University, 5-1 Anam-Dong, Sungbuk-Ku, Seoul 136-701, Korea, KR;(2) Department of Statistics, Ewha Womans University, 1 Daehyun-Dong, Seodaemun-Ku, Seoul, 120-750, Korea, KR
Abstract:
Received: April 3, 2000; revised version: November 6, 2000