0: Test for source tree numbering 0: Level A 0: Level B 0: Level B, again 0: Level C 0: Level B 0: Level C 0: Level D 0: Level C 0: Level C, again 0: Level A 0: Level B 0: Level C 0: Level D 1: Level E 1: Level A 0: Level B 0: Level C 0: Level D 1: Level E 2: Level E, again 0: Level D 1: Level E 1: Level C 0: Level D 0: Level B