use Data::Dumper;
use Storable qw/dclone/;

my @a = (1,2,3,4,6);
$Data::Dumper::Indent=0;
print Dumper(increment(increment(\@a))), "\n";

sub increment{
   my $d = shift;
   my @b;
   for my $i (1..$#$d){
      my @a = @$d[$i-1..$i];
      push @b, dclone \@a;
   }
   return \@b;
}

__END__

$VAR1 = [[[1,2],[2,3]],[[2,3],[3,4]],[[3,4],[4,6]]];