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Aucb.379 fa.editor-p utcsrgv!utzoo!decvax!ucbvax!CAD:ARPAVAX:C70:editor-people Fri Feb 5 16:18:45 1982 Undo >From ZIMMER@DEC-MARLBORO Fri Feb 5 16:12:46 1982 The prototype version of Etude allowed a single-step undo. Everything could be undone except for file manipulation operations. The underlying implementation could have handled a multiple-step undo, but the user interface didn't handle it.

Single-step undo isn't sufficient for good error recovery; see the example of "edit" in Bravo mentioned a few messages ago. The questions about how to do multiple-step undo are good. We really need some experimental evidence to guide us in this area.

Undo is handy not only as an error-correction aid, but also as a way to encourage people to experiment with a system. When someone asks "What does this do?" you can say "Try it; if you don't like it you can always undo it." This approach was used in Etude's tutorial.

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