s 3
t 3
( s 1 , s 2 )
(11, 5)
(7, 3)
( t 1 , s 2 )
(6, 3)
(9, 7)
( s 1 , t 2 )
(−1, 4)
(5, 4)
( t 1 , t 2 )
(4, 4)
(1, 5)