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print "number of vertices: ".$G->vertices."\n";
print "number of edges: ".$G->edges."\n";
...
print "Name of edge E1->E2 is ".$G->get_attribute("name","E1","E2")."\
+n";
print "Name of edge E2->E3 is ".
      (defined $G->get_attribute("name","E2","E3") ? $G->get_attribute
+("name","E2","E3") : "<undef>") ."\n";

             @V = $G->vertices

...
       of the vertices @v if the vertex exists in the graph $G
       and undef if it doesn't.  In scalar context returns the
       number of the existing vertices.