All edges are hard boundaries.The top and bottom edges are hard boundaries, but the left and right edges are connected to each other. (Cylinder world)The top and bottom edges are connected to each other, as well as the left and right edges.The top and bottom edges are hard boundaries and the left and right edges are connected in reverse.The top and bottom edges are connected to each other and the left and right edges are connected in reverse.The top and bottom edges as well as the left and right edges are pair-wise connected in reverse.