6 exit: ( 0 0 c ) ( 10 0 x ) ( 29 10 a )
8 ( 19 20 w ) ( 0 10 d ) ;
10 beacon: ( 10 10 ) ( 19 10 ) ;
12 airport: ( 15 15 x ) ;
14 line: [ ( 1 1 ) ( 9 9 ) ]
17 [ ( 11 10 ) ( 18 10 ) ]
18 [ ( 15 11 ) ( 15 14 ) ]
19 [ ( 20 10 ) ( 28 10 ) ]
20 [ ( 19 11 ) ( 19 19 ) ]
21 [ ( 20 11 ) ( 28 19 ) ] ;