graph G {
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  node [fontname="Helvetica"];
  edge [fontname="Helvetica"];
  a1 [shape=circle, label="C", width=0.46, height=0.46, fixedsize=true, style="filled", fillcolor="white", color="#111827", penwidth=1.4];
  a2 [shape=circle, label="C", width=0.46, height=0.46, fixedsize=true, style="filled", fillcolor="white", color="#111827", penwidth=1.4];
  h1 [shape=circle, label="", xlabel="", width=0.10, height=0.10, fixedsize=true, style="filled", fillcolor="#111827", color="#111827", fontcolor="#6b7280", fontsize=9];
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  h2 [shape=circle, label="", xlabel="", width=0.10, height=0.10, fixedsize=true, style="filled", fillcolor="#111827", color="#111827", fontcolor="#6b7280", fontsize=9];
  a2 -- h2 [style=dashed, color="#9ca3af", penwidth=1.0];
}