The nested lists are forming a parent-child relationship based on a set of keys.
嵌套列表基于一组键形成父子关系。
Note that the inv function USES SPL nested lists to represent matrices, as there is no matrix type in SPL.
请注意，inv函数使用SPL嵌套列表来表示矩阵，因为SPL中没有矩阵类型。
As you can see from Listing 7, additional nested lists are embedded into the list item elements for Workgroups and Conferences.
正如在清单7中看到的，额外的嵌套列表被嵌入Workgroups和Conferences的列表项元素。
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