==== The Zipper ====

"Zipper is a very handy [[Data Structure]] that lets us replace an item deep in a complex data structure, e.g., a tree or a term, without any mutation." --Oleg Kiselyov

  * http://www.nist.gov/dads/HTML/zipper.html
  * [[ZipperOS]]
  * [[Zipper In Scheme]]