How to reconnect a split face to its mesh? I have accidentally pressed the Y key and have split a face from its mesh.

I can undo the action but I would like to know the actual command to do the opposite of split.

Merge tool options did not work (unless I am doing it wrong).
Object mode -> Join did not work.
Being in Edit Mode select the whole mesh (A), hit W-->Remove Doubles. Now you have a consistent mesh.


You may also use a Undo History pop up menu (press Ctrl+Alt+Z) and select the step you want to get back to.