"[[[[a,b],c],[d,e]],[f,g]]"
(0, (1, 19)) (1, (2, 12)) (2, (3, 9)) (3, (4, 6)) (4, (a, 5, 5)) (5, (8, 8)) (6, (b, 7, 7)) (7, (8, 8)) (8, (11, 11)) (9, (c, 10, 10)) (10, (11, 11)) (11, (18, 18)) (12, (13, 15)) (13, (d, 14, 14)) (14, (17, 17)) (15, (e, 16, 16)) (16, (17, 17)) (17, (18, 18)) (18, (25, 25)) (19, (20, 22)) (20, (f, 21, 21)) (21, (24, 24)) (22, (g, 23, 23)) (23, (24, 24)) (24, (25, 25)) (25, (0, 0)) (26, (0, 0))