Undo and Redo Function

There should be two buttons, one for Undo and one for Redo. When you press the Undo button, the last action you habe performed will be taken back. Action can be a format action, writing or deleting some text etc. This is extremely helpful, because on the touch screen it is even easier to cause undesired effects. Since you cannot quit withou saving, you can easily spoil your documents. Without Undo it is hard to work productively. Redo just repeats the last action. Can be limited to actions undone previously.