my %hash;
@hash{ 3,4 } = qw( perl hacker );
print join ",", keys %hash;      # prints "3,4"

##</code><code>##

my %hash;
$hash{ 3,4 } = qw( perl hacker );
print join ",", keys %hash;      # ????

##</code><code>##

my %hash;
$hash{ (3,4) } = qw( perl hacker );
print join ",", keys %hash;      # ????

##</code><code>##

my %hash;
$hash{ [3,4] } = qw( perl hacker );
print join ",", keys %hash;      # ????

##</code><code>##

my %hash;
$hash{ 3,4 } = qw( perl hacker );
print $hash{ 3,4 }, "\n";

##</code><code>##

my %hash;
for my $i (0..5) {
  for my $j (0..5) {
    $hash{ $i,$j } = $i*$j;
  }
}
foreach ( keys %hash ) { print "$_ : ", $hash{ $_ }, "\n"; }

##</code><code>##

grep { nth_element_of_the_key eq 'test' } keys %hash;