Php app using strtolwer(); function

<?php

 if (isset($_GET['user_name']) or !empty($_GET['user_name'])) {
   $user_name =$_GET['user_name'];
   $user_name_lc = strtolower($user_name);
   
   if($user_name_lc=='waqas') {
   echo '<strong>Well come!</strong> '.$user_name;
   }
   
}

?>
<form action="app1.php" method="get">
Name: <input type="text" name="user_name"></br>
<input type="submit" value="submib">
</form>