ALT+BKSP, SHIFT+CTRL+BKSP
Undo
Reverses the last editing operation. The maximum number of times this can be performed for each file is set by the Undocount switch.
Meta Undo (F9 ALT+BKSP)
Performs the operation previously reversed with Undo. This action is often called “redo.”
TrueOperation undone or redone.
FalseNothing to undo or redo.
_pwbundo, _pwbredo, Repeat