sub make_singular {
  my $word = shift;
  $word =~ s/s$//;
  
  my @in_sub_filesize_names = @filesize_names; # added this line, the output is still wrong.
  my @short_sizes = map(s/^(\w)\w{1,}$/$1b/,@in_sub_filesize_names);
  if (grep(/\L$word\E/,@short_sizes)) {
    $word = $filesize_names[firstidx { $_ eq lc $word} @short_sizes];
  }
  
  return lc $word;
}