my $i = 0;
  use constant PCHR => split //, 'KQRBNP';
  my %pchr = map { $_ => $i++ } PCHR;
  my $w1 = 'QRKPNB';
  my $w2 = join '', sort { $pchr{$a} <=> $pchr{$b} } split //, $w1;
  print "$w1 -> $w2\n";