当您使用to运算符迭代各个整数时，上下文item(2.0中的上下文item)是未定义的。
As you use the to operator to iterate through various integers, the context item (it's the context item in 2.0) is undefined.
不能存在以下情况：相等运算符或不等运算符适用于某类型的实例，却未定义相反运算符。
There are no circumstances where either equality or inequality is applicable to instances of a type, and the opposite operator is undefined.
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