When three tiles surround an empty space so that it is effectively half covered this is called a "forced" space. If the person whose turn it is has a tile that fills that space they must play it. The player repeats this process until there are no more forced spaces that they can fill, at which stage they make a free move, where they can play any tile as long as they don't breach the three restriction rules given below. Once they have had a free move, they must then fill any more forced spaces that they can. Thus one player's turn can consist of several moves.