Fatal error: Call to undefined function inarray() คืออะไรครับ

<?PHP
session_start();
$product_id=$_GET[id];

if (count($sess_id)=="0") {
	$check=1;
} else if (!inarray($product_id , $sess_id)){
	$check=1;	
}
if ($chaek=1) {
	include('webadmin/connect.php');
	$sql="SELECT
cart_product.product_id,
cart_product.cart_id,
cart_product.product_code,
cart_product.product_name,
cart_product.description,
cart_product.photo,
cart_product.type,
cart_product.price_send,
cart_product.price,
cart_product.date_post
FROM
cart_product where product_id='$product_id'";
$query=mysql_query($sql);
$rs=mysql_fetch_array($query);

$sess_product_id[]=$rs[product_id];
$sess_cart_id[]=$rs[cart_id];
$sess_product_code[]=$rs[product_code];
$sess_product_name[]=$rs[product_name];
$sess_price[]=$rs[price];
$sess_num[]=1;

//session_register();
$_SESSION['sess_product_id']=$sess_product_id;
$_SESSION['sess_cart_id']=$sess_cart_id; 
$_SESSION['sess_product_code']=$sess_product_code;
$_SESSION['sess_product_name']=$sess_product_name;
$_SESSION['sess_price']=$sess_price;
$_SESSION['sess_num']=$sess_num;

}

header("Location: basket.php");

?>