let open = {(0,0)}
open.remove( (0, 0) )
(1, 0) not in open
open.add( (1, 0) )
(0, 1) not in open
open.add( (0, 1) )
open.remove( (0, 1) )
(1, 1) not in open
open.add( (1, 1) )
(0, 2) not in open
open.add( (0, 2) )
open.remove( (1, 0) )
(2, 0) not in open
open.add( (2, 0) )
open.remove( (2, 0) )
(3, 0) not in open
open.add( (3, 0) )
(2, 1) not in open
open.add( (2, 1) )
open.remove( (1, 1) )
(1, 2) not in open
open.add( (1, 2) )
open.remove( (0, 2) )
(0, 3) not in open
open.add( (0, 3) )
open.remove( (2, 1) )
(3, 1) not in open
open.add( (3, 1) )
(2, 2) not in open
open.add( (2, 2) )
open.remove( (3, 0) )
(4, 0) not in open
open.add( (4, 0) )
open.remove( (0, 3) )
(1, 3) not in open
open.add( (1, 3) )
print((0, 4) not in open)
open.add( (0, 4) )
open.remove( (1, 2) )
open.remove( (2, 2) )
print((3, 2) not in open)


print("done")