Zipper like data structure with more than one cursor

Question

The Zipper data structure is great when one wants to traverse a tree and keep the current position, but what data structure one should use if they want to track more then on

Answer 1

See this paper . I seem to recall reading somewhere that the second derivative has two holes, which is probably what you want.

Answer 2

Oleg's work on "concurrent" zippers via delimited continuations is the main reference.