my $result= Graph::Undirected->new();
foreach my $edge_ac ($g->edges()) {
+ $result->add_vertex($edge_ac->[0]); # just in case
next if $edge_ac->[0] eq $edge_ac->[1];
my $edgename_ac= join ' .. ', @$edge_ac;
printf DEBUG "spr %s edge %s\n", $what, $edgename_ac;