#### Location of the documentation https://pandas.pydata.org/pandas-docs/stable/reference/indexing.html #### Documentation problem Index is described as a "set", but behaves as a multiset: len() counts each occurrent of a duplicate element separately. Also, Index is described as an "ordered set", but that term connotes a set with an order relation on the _values_ of its elements. #### Suggested fix for documentation An index seems more like an immutable ordered _list_; maybe, describe it as that?