digraph {

        start [label="C:\nCode\nManagement" style="dotted"]
        {rank=same; start S0}
        start -> S0 [style="invis"]
        S0 [label="S0:\nidle"]
        S0 -> P0_got_code [label="set_code"]
        P0_got_code [shape="box" label="B.got_code"]
        P0_got_code -> S3
        S3 [label="S3: known" color="green"]

        {rank=same; S1_inputting S2_allocating}
        S0 -> P_input [label="input_code"]
        P_input [shape="box" label="I.start"]
        P_input -> S1_inputting
        S1_inputting [label="S1:\ninputting"]
        S1_inputting -> P0_got_code [label="finished_input"]

        S0 -> P_allocate [label="allocate_code"]
        P_allocate [shape="box" label="A.allocate"]
        P_allocate -> S2_allocating
        S2_allocating [label="S2:\nallocating"]
        S2_allocating -> P1_generate [label="allocated_nameplate"]
        P1_generate [shape="box" label="generate\nrandom words"]
        P1_generate -> P0_got_code

}