\x89\x50\x4E\x47\x0D\x0A\x1A\x0A
 PNG

\x89\x50\x4E\x47\x0D\x0A\x1A\x0A
/* Add edges from input graph to argument graph
 * Does not add nodes.
 */
BEGIN{
  graph_t g = readG(ARGV[0]);
  node_t h, t;
  edge_t e;
}
E {
  if ((h = isNode(g,head.name)) && (t = isNode(g,tail.name))) {
    if (!isEdge(t,h,"")) {
      e = copy(g,$);
    }
  }
}
END {
  write(g);
}