digraph g {
  edge [arrowhead=none];


  node [shape=circle,width=0.5,fixedsize=true];   
  subgraph cluster_b {
    b1 [label=<B<SUB>1</SUB>>];
    b0 [label=<B<SUB>0</SUB>>];
  }

  subgraph  cluster_c {
    c1 [label=<C<SUB>1</SUB>>];
    c0 [label=<C<SUB>0</SUB>>];
  }

  graph [style=dashed, color=grey]
  node [shape=cbox,width=0.5,fixedsize=true];   
  subgraph cluster_gb {
    gbi [label=<G<SUB>B,i</SUB>>];
    gb0 [label=<G<SUB>B,0</SUB>>];
  }
  subgraph cluster_gc {
    gci [label=<G<SUB>C,i</SUB>>];
    gc0 [label=<G<SUB>C,0</SUB>>];
  }
  subgraph cluster_f {
    f0 [label=<F<SUB>0</SUB>>];
    fi [label=<F<SUB>i</SUB>>];
  }

  graph [style="",color=""]
  node [shape=circle,width=0.5,fixedsize=true];   

edge [penwidth=2.3]
b0->gb0;
b0->gbi;
b1->gb0;
b1->gbi;

c0->gc0;
c0->gci;
c1->gc0;
c1->gci;
edge [penwidth=""]

gb0->f0;
gbi->fi;
gc0->f0;
gci->fi;

  subgraph cluster_d {
    di [label=<D<SUB>i</SUB>>];
    d0 [label=<D<SUB>0</SUB>>];
  }

f0->d0;
fi->di;






}