s 2
t 2
( s 1 , s 3 )
(11, 5)
(5, −2)
( t 1 , s 3 )
(7, 2)
(7, 1)
( s 1 , t 3 )
(9, 1)
(8, 1)
( t 1 , t 3 )
(10, 6)
(6, 0)