struct cell {
		struct cell *links[4]; // up, down, left, right
		int data;
	};

	struct cell cell_ul;
	struct cell cell_ur;
	struct cell cell_ll;
	struct cell cell_lr;
	struct cell cell_ul = { { 0, &cell_ll, 0, &cell_ur } };
	struct cell cell_ur = { { 0, &cell_lr, &cell_ul, 0 } };
	struct cell cell_ll = { { &cell_ul, 0, 0, &cell_lr } };
	struct cell cell_lr = { { &cell_ur, 0, &cell_ll, 0 } };