my %hash = ();
my $hashref = \%hash;
%hash = (
           key1 => { key1_1 => ["value1_1",value1_2"],
                     key1_2 => "w00t!",
                   },
           key2 => { key2_1 => "wakkawak!", 
                     key2_2 => $hashref->{key1}{key1_1}, 
                   },
           );