rest of emacs under ransom or else undo the undos

[Dan Jacobson]

What happens when you get halfway thru where you need to hit undo
[C-/] many times, and the phone rings and you need to check another
buffer momentarily... doing this resets the undo mode, and when you
return to hitting undo you are now undoing the undos... there should
be a away not to keep the whole rest of emacs under ransom else risk
reseting the undos.
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