T1
t2
1.1
1.2
2.1
2.2
3.1
3.2
4.1
4.2
t3
t4
1.3
1.4
2.3
2.4
3.3
3.4
4.3
4.4
t5
t6
1.5
1.6
2.5
2.6
3.5
3.6
4.5
4.6