use strict;
use warnings;
use Data::Dumper;

my @a = (1, 2, 3, 4, 6);
my $y = increment(increment(\@a));

for my $j (@$y)
{
    print "[\n";

    for my $k (@$j)
    {
        print "    $k: @$k\n";
    }

    print "]\n";
}

sub increment
...