+            $step+         $step   +      $step      +
           $Co$W    $S    $Co$W    $S    $Co$W    $S    $Co$W
       $z           $L $z         $L   $z       $L     $z 
     $W     $L        $W     $L        $W     $L        $W
                                                          
    +                 +                 +                 +