mark.umcp-cs@UDel-Relay@sri-unix (09/11/82)
From: Mark Weiser <mark.umcp-cs@UDel-Relay> Yes. I think losing the Meta key by redefinition is a red herring. This can always be worked around by reserving a meta valid in all universes. I think you stated the basis for a mathematical theory of meta and undo in your letter: time. (Shades of Heidegger and existential philosophy!) A meta level has a very simple relation to the previous levels: it freezes the previous level as a closed universe with all times spread out on the time line, and then allows editing at any point in that time (with subsequent causality edited implicitly). Meanwhile, "real" time moves to the new meta universe where the past is immutable and the future flexible (until meta is struck again...). Mathematically I think everything will be fairly simple since computers are mathematically trivial (finite state machines and all that). About implicit causality editing: should the future vanish as the past is edited, or should as much of the future be preserved as possible, consistent with the edit?