notes hashing is well-studied technique the reader interested in further study is encouraged to explore the book by knuth [ ]as well as the book by vitter and chen [ skip lists were introduced by pugh [ our analysis of skip lists is simplification of presentation given by motwani and raghavan [ for more in-depth analysis of skip listsplease see the various research papers on skip lists that have appeared in the data structures literature [ exercise - was contributed by james lee