sub edges2vertices {
  #AoA to uniq array elem;

  my @edges = @_;
  my @vertices;
  my @uniqv; 
  
   for my $i ( 0 .. $#edges ) {
               for my $j ( 0 .. $#{$edges[$i]} ) {
                   push @vertices, $edges[$i][$j];
               }
           }

       @uniqv = sort keys %{{map {$_,1} @vertices}};
    return @uniqv;
}