1 Line_1_3 Line_3_3 Line_4_3 
2 Line_2_3 (empty)  Line_5_3
3 (empty)  (empty)  Line_6_3
4 (empty)  (empty)  Line_7_3
.    .        .         .
.    .        .         .
.    .        .         .
n Line_n_3 Line_n_3 Line_n_3[n]