A little help with php

I have installed the recipe module. In this module there is a control that makes it impossible to write the same ingredient two times. I want to get rid of this control. The code is down here. Anyone who can tell me how to change the code to take away that control?

function recipe_ingredients_diff($a1,$a2) {
  $return->add = array();
  $return->remove = array();
  $return->update = array();

  foreach ($a1 as $pl) {
    $pl = (object)$pl;
    $pl->name = trim($pl->name);
    if ($pl->name) {
      if (!_in_array($pl,$return->add)) {
        // Duplicate entries for the same ingredient are ignored.
        if (!_in_array($pl, $a2))
          $return->add[] = $pl;
        else
          if (!_in_array($pl,$return->update))
            $return->update[] = $pl;
      }
    }
  }
  foreach ($a2 as $k => $pl) {
    if (!_in_array($pl, $a1)) {
      $return->remove[] = $pl->id;
    }
  }
  return $return;
}