This expression is used inside the braces {} that define the index of the summation. The syntax for an expression is
这个表达式在花括号（{}）中使用，它定义了和的索引。
2
Since a dummy index just indicates summation, it is immaterial which symbol is used.
由于哑指标只是表明求和，所以它使用什么符号是无关重要的。
3
Then in the index compared Linklist have the same index, if the same index, then the corresponding coefficient for peace, and the summation of the results of merging llist2;