use Data::Dumper qw/Dumper/;
my %a = map { $a{$_} => 1 unless undef, 0..5 } 0..11;
print Dumper \%a;

##</code><code>##

$VAR = {
'11' => 12,
'1' => 2,
'3' => 4,
'7' => 8,
'9' => 10,
'5' => 6
};
##</code><code>##

my %a = map { $a{ $a{ $a{ $a{ $a{ $_ } } } } } => 1, 0..5 } 0..9;
print Dumper sort(\%a);

##</code><code>##

my %a = map { $a{ $_ } => 1, 0..5 } 0..9;