digraph {
  s  [ shape="box",  label="[0] Request" ];
  p  [ shape="box",  label="[A] Pass" ];
  b  [ shape="box",  label="[B] Block" ];
  t  [ shape="oval", label="[6] Set new token" ];
  c  [ shape="oval", label="[4] Show captcha" ];
  w  [ shape="oval", label="[3] Some heavy\noperation" ];
  i  [ shape="oval", label="[9] Accounting" ];
  rl [ shape="diamond", label="[8] Is rate-limit\nexceeded?" ];
  ht [ shape="diamond", label="[1] Has token?" ];
  vt [ shape="diamond", label="[2] Is token valid?" ];
  cv [ shape="diamond", label="[5] Is captcha valid?" ];
  ts [ shape="diamond", label="[7] Is token set?" ];

  s  -> ht [ style="bold", weight=2 ];
  ht -> vt [ label="Y", style="bold", weight=2 ];
  ht -> w  [ label="N", style="dashed" ];
  w  -> t  [ style="dashed" ];
  t  -> ts [ style="solid" ];
  ts -> b  [ label="N" ];
  ts -> p  [ label="Y", style="solid" ];
  vt -> rl [ label="Y", style="bold", weight=2 ];
  rl -> i  [ label="N", style="bold", weight=2 ];
  i  -> p  [ style="bold", weight=2 ];
  rl -> b  [ label="Y", style="bold" ];
  vt -> c  [ label="N" ];
  c  -> cv;
  cv -> c  [ label="N" ];
  cv -> t  [ label="Y" ];
}