Kent Pitman's paper has moved to a new home URL:
This paper was originally written as an HTML document, exactly as shown below. Any final reformatting that was done for hardcopy publication in LaTeX may have been lost in this version. Any new text that has been added for this annotated version appears bracketed and in color green; such text is intended to help clarify the historical context as time passes.
--Kent Pitman, 28-Feb-2002.