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 my @a=2..44;
 egrep { $prev =~/4$/ or $next =~/2$/ } @a;  # 5, 11, 15, 21, 25, 31, 35, 41
 egrep { $prevr=~/4$/ or $nextr=~/2$/ } @a;  # 2, 5, 11, 15, 21, 25, 31, 35, 41, 44
 egrep { $i%7==0 } @a;                       # 2, 9, 16, 23, 30, 37, 44
 egrep { $n%7==0 } @a;                       # 8, 15, 22, 29, 36, 43

=cut

sub egrep (&@) {
    my($code,$i,$package)=(shift,-1,(caller)[0]);
    my %h=map{($_=>"${package}::$_")}qw(i n prev next prevr nextr);
    no strict 'refs';
    grep {
	#no strict 'refs'; #not here! "no" not allowed in expression in perl5.16
	local ${$h{i}}     = ++$i;
	local ${$h{n}}     = $i+1;
	local ${$h{prev}}  = $i>0?$_[$i-1]:undef;
	local ${$h{next}}  = $i<$#_?$_[$i+1]:undef;
	local ${$h{prevr}} = $_[$i>0?$i-1:$#_];
	local ${$h{nextr}} = $_[$i<$#_?$i+1:0];