[(0,1),(1,2),(2,3),(1,3),(0,4),(3,5),(5,6),(2,6),(6,7),(4,7),(4,8),(7,8),(5,9),(9,10),(10,11),(11,12),(12,13),(11,13),(9,14),(8,15),(12,16),(10,17),(13,18)]
[(0,1),(1,2),(0,2),(1,3),(2,3),(3,4),(4,5),(5,6),(6,7),(5,7),(6,8),(7,8),(8,9),(4,10),(10,11),(10,12),(11,12),(9,13),(11,14),(12,15),(9,16),(13,17),(13,18)]
