1l1_4 2l1_5 3l1_6 4l1_7 5l1_8 6l1_9 7l1_10 8l1_11 9l1_12 10l1_13 11l1_14 12l2_1 13l2_2 14l2_3 15l2_4 16l2_5 17l2_6 18