The second, embedded combination of sum and EXTRACT function calculates the lower boundary, which is based on the sum of values in preceding slices, represented in the map rule as InSliceIndex - 1.

嵌套的第二个SUM和EXTRACT函数组合计算下限，下限基于前面的片中的值的总数，在映射规则中表示为InSlice Index - 1。

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