* The I n stitute o f Scie ntific and Industria l Re search , Osaka University , 8 -l Mihogaoka , Ibaragi , Osaka 7 , Japan; Fac ulty o f Eng inee ring , Os aka Uni versity , 2-1 Yamada oka , Suita , Os a k a 565 , Japa
1 paper in the IJCAI proceedings
