Simple Simple Noob Question

[The_MA]

Below is a simple session. At the moment it checks for the session 'admin'. I would like it to check for either 'admin' OR 'user'

thanks in advance. x

session_start();

if (!isset($_SESSION['admin']) 
   || $_SESSION['admin'] !== true) {

   header('Location: login.php');
   exit;
}

[Kudose]

session_start();
if(!isset($_SESSION['admin'] && !isset($_SESSION['user']))
  header("Location: login.php");
else
  echo 'Either an admin or user session is set.';

[rincewind456]

session_start(); 

if (!isset($_SESSION['admin']) || $_SESSION['admin'] !== true ||  (!isset($_SESSION['user']) || $_SESSION['user'] !== true)) { 

   header('Location: login.php'); 
   exit; 
}