This is an extended version of an informal and anecdotal talk that I gave at Grinnell College on March 16, 2001, and again (with revisions) on April 13, 2005 and on February 12, 2009.
This document is available on the World Wide Web, beginning at
http://www.cs.grinnell.edu/~stone/essays/keeping-stuff/
This work is licensed under a Creative Commons Attribution-ShareAlike 3.0 United States License.
created March 11, 2001
last revised February 10, 2009