sub inc{
   my $ref=shift;
   my $span=shift;
   $span?($span--):($span=1);

   my @b=map{ clone([@$ref[$_-$span..$_]])  }($span..$#$ref);

   \@b
}
sub clone{#clone references
   my $ref=shift;
   my@array=map{ ref($_)?clone($_):$_ }@$ref;
   \@array
}
my@b=(1..5);
my $c = inc(inc(\@b));
print Dumper $c;