title: Purely functional concurrent skip list
body: <p><a href="ftp://ftp.cs.umd.edu/pub/skipLists/skiplists.pdf" rel="noreferrer">Skip lists</a> (Pugh, 1990) provide sorted dictionaries with logarithmic-time operations like search trees but <a href="http://www.cl.cam.ac.uk/research/srg/netos/lock-free/" rel="noreferrer">skip lists are much more amenable to concurrent updates</a>.</p>
  
  <p>Is it possible to create an efficient purely functional concurrent skip list? If not, is it possible to create any kind of efficient purely functional concurrent sorted dictionary?</p>