J.D.L. Caro, Dept. of Math., Univ. of the Philippines, Quezon City, Philippines L.R. Nochefranca, Dept. of Math., Univ. of the Philippines, Quezon City, Philippines P.W. Sy, Dept. of Math., Univ. of the Philippines, Quezon City, Philippines F.P. Muga, II, Dept. of Math., Univ. of the Philippines, Quezon City, Philippines