Mediator in tic-tac-toe

As I know ,, mediator is a design pattern to control many to many realationships among other classes. And I'm trying to use it in a tic tac toe game for the purpose of Undo and Redo (I need to do so). I've got an abstract class : Level that contains an array of object of Board . This Board is another class containing a 2D array (3x3) of cells. Do I need to create a mediator somehow or its applied implicitly ? Thanks in advance.