sub _nsc
{
    my @a = @{$_[0]};
    my @b = @{$_[1]};
    @a && @b or return( @a ? 1 : @b ? -1 : 0 );
    my $x = shift @a;
    my $y = shift @b;
    $x =~ /\d/ ? ( $y =~ /\d/ ? length($x)<=>length($y)
    || $x <=> $y || _nsc(\@a,\@b) : -1 ) : ( $y =~ /\d/
    ? 1 : lc($x) cmp lc($y) || _nsc(\@a,\@b) )
}