A few comments...

The add() method is still there, I believe that a method to insert without giving an index is useful in a sequence.

The insert and delete methods are not named _insert and _delete, this has three reasons. 1) There is currently no lfun insert and delete. 2) I belive that it should be possible to remove and insert without using and lfun 3) If there will be a insert and delete lfun then it should not be difficult to use the current insert and delete methods.

A few words about the coming ADTs It will probably be an ordered map maybe a sequence, a set, a priority list and a heap, based on a binary tree and a sequence, a queue and a stack based on a double linked list and finally wrappers for mapping, multiset and array.