为了讨论方便起见,现将平均收敛的概念叙述如下: 设 f_1,f_2,……,f_n,……和f都是可测集E上的平方可积函数,如果对于任意的正数ε,有N,当n>N时,不等式 ||f_n-f|| <ε成立,则称f是{f_n}的极限,也可以说{f_n}收敛于f,记作 用正常的函数论的话来说,的意思是(?) For the sake of discussion, the concept of average convergence is now described as follows: Let f_1, f_2, ..., f_n, ..., and f be square integrable functions on the measurable set E, if for any positive number, we have N, when n> N, the inequality || f_n-f || <ε holds, then f is called the limit of {f_n}, that is to say {f_n} converges to f, and in the words of normal function theory, means(?)