graph G {
  graph [layout=neato, overlap=false, splines=true, outputorder=edgesfirst, bgcolor="white", pad=0.12, labelloc="t", label="Rule K: atom interface", fontname="Helvetica"];
  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];
}