: Test for source tree numbering *1*: Level A *1+1*: Level B *1+2*: Level B *1+2+1*: Level C *1+3*: Level B *1+3+1*: Level C *1+3+1+1*: Level D *2*: Level A *2+1*: Level B *2+1+1*: Level C *2+1+1+1*: Level D *2+1+1+1+1*: Level E *3*: Level A *3+1*: Level B *3+1+1*: Level C *3+1+1+1*: Level D *3+1+1+1+1*: Level E *3+1+1+2*: Level D *3+1+1+2+1*: Level E *3+1+2*: Level C *3+1+2+1*: Level D *3+2*: Level B