Undo and redo are two of the most basic editing operations. You can invoke them with either toolbar buttons or gestures.
Undo is the equivalent of a backspace key for your ink input – as you write, you can use undo to erase your last stroke, the way you use the backspace key to erase the last typed character. You can also undo recognition and editing operations, but you cannot undo preference changes.
Redo restores writing and any editing steps that you reversed with undo.