- https://www.csee.umbc.edu/courses/undergraduate/341/fall01/Lectures/SkipLists/skip_lists/skip_lists.html
- http://eternallyconfuzzled.com/tuts/datastructures/jsw_tut_skip.aspx
- http://ticki.github.io/blog/skip-lists-done-right/
notes: something like a DAG compressed by a popcount'd bitmap for each tree node's children, shrunken even further by the observation that only certain bitmaps will be needed for a given language (in this case, english)