root    HASH (0           ): { nc => 0, top_foo => 1 }
    a    HASH (0:0         ): { nc => 1 }
    b    HASH (0:0:0       ): { nc => 2 }
    e    HASH (0:0:1       ): { nc => 3 }
    f    HASH (0:0:1:0     ): { nc => 4 }
    g    HASH (0:0:1:0:0   ): { nc => 5 }
    c    HASH (0:0:2       ): { nc => 6 }
    d    HASH (0:0:2:0     ): { nc => 7 }
    h    HASH (0:1         ): { nc => 8 }
    i    HASH (0:1:0       ): { nc => 9 }
    j    HASH (0:1:0:0     ): { nc => 10 }