use Data::Dumper;
$Data::Dumper::Indent = 1;

my @remove;
while (%depend) {
  # Clear dependencies
  foreach my $dep (values %depend) {
    @$dep = grep {exists $depend{$_}} @$dep;
  }

  # What can I remove?
  my @can_remove = grep {0 == @{$depend{$_}}} keys %depend; 
  if (@can_remove) {
    delete $depend{$_} foreach @can_remove;
    push @remove, @can_remove;
  }
  else {
    # Uh, oh
    print "CIRCULAR DEPENDENCIES DETECTED\n";
    print Data::Dumper->Dump ([\%depend], ['*depend']);
    die "ABORTING";
  }
}
print Data::Dumper->Dump([\@remove], ['*remove']);