digraph g {
  graph[rankdir="LR" dpi=300];
  node[shape=circle];
  n1 [label="●"];
  t1 [shape=rect height=0.4 width=0.03 color=black bgcolor=black label="" style=filled xlabel=<b<SUB>l</SUB>(x)>];
  t2 [shape=rect height=0.4 width=0.03 color=black bgcolor=black label="" style=filled xlabel=<u<SUB>l</SUB>(x)>];
  n2 [label=" "];
  n1 -> t1;
  {rank = same; t1 -> t2 [style=invis]};
  t2 -> n1;
  t1 -> n2;
  n2 -> t2;
}