两个集合，两个函数 If we are to develop efficient error-detecting and error-correcting codes,we will need more sophisticated mathematical tools.Group theory will allow faster methods of encoding and decoding messages.A code is an (n,m)- block code if the information that is to be coded can be divided into blocks of m binary digits,each of which can be encoded into n binary digits.More specifically,an (n,m)-block code consists of an encoding function E:Z→Z5 and a decoding function D:z→Z. 问题6 顺便问一下；为什么这里说群论会给我们很大带助？两个集合，两个函数