{ package RecMy ;

  use strict ;

sub rec {
  my $n = shift ;
  return if !$n ;
  
  rec( --$n ) ;

  my $local = "[$n] set" if ($n/3) !~ /\./ ;
 
  $local .= ' append' ;
  
  print "<$n> $local\n" ;

}

  for(1..5) {
    print "--------------------- $_\n" ;
    rec(4);  
  }
}

##</code><code>##

--------------------- 1
<0> [0] set append
<1>  append
<2>  append
<3> [3] set append
--------------------- 2
<0> [0] set append
<1>  append append
<2>  append append
<3> [3] set append
--------------------- 3
<0> [0] set append
<1>  append append append
<2>  append append append
<3> [3] set append
--------------------- 4
<0> [0] set append
<1>  append append append append
<2>  append append append append
<3> [3] set append
--------------------- 5
<0> [0] set append
<1>  append append append append append
<2>  append append append append append
<3> [3] set append

##</code><code>##

--------------------- 1
<0> [0] set append
<1>  append
<2>  append
<3> [3] set append
--------------------- 2
<0> [0] set append
<1>  append
<2>  append
<3> [3] set append
--------------------- 3
<0> [0] set append
<1>  append
<2>  append
<3> [3] set append
--------------------- 4
<0> [0] set append
<1>  append
<2>  append
<3> [3] set append
--------------------- 5
<0> [0] set append
<1>  append
<2>  append
<3> [3] set append

##</code><code>##

  ## changed from (bugged):
  my $local = "[$n] set" if ($n/3) !~ /\./ ;

  ## to (fine):
  my $local ;
  $local = "[$n] set" if ($n/3) !~ /\./ ;

##</code><code>##

... if ($n/3) !~ /\./ ;