设计文法类，实现对文法G[S]=(Vt, Vn, P, S)的文件读写，文法的文件表示形式以及内存表示形式可自定义。本质上，文法就是3个集合+1个符号，重点（难点）是产生式集合如何处理。文法的文本形式可根据自己需要自由定义。在前述的基础上，实现文法化简的无用符号及无用产生式消除算法。

-Grammar class design, to achieve the grammar G [S] = (Vt, Vn, P, S) to read and write files, grammar files and memory representation of representation can be customized. In essence, the grammar is a collection of three+1 symbols Key (difficulty) is a collection of how to handle the production. Text grammar can be freely defined according to their own needs. In the foregoing, based on the realization of grammar simplification useless symbols and useless productions cancellation algorithm.