1 1 f f f n : ((...( ) ¾¾®a f 1 a ) ¾¾® ,...a ) ¾¾®a ) 1 2 n - 1 n f -n : (a 0 ¬¾¾ ( ¬¾¾a 1 f - 1 ,...,¬¾¾ ( ))a n - - 1 1 f f