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