More readable approach?
You can rewrite it like this:

// you have to be in both 'group' and 'board' to get access
$has_access = $is_in_group &amp;&amp; $is_in_board;
// you must have access or be a superuser
if (!($has_access || $is_superuser)) die('No access');


I don't think an explanation is needed.

Alternatively you could even write:

// you have to be in both 'group' and 'board' to get access
$has_access = $is_in_group &amp;&amp; $is_in_board;
// you must have access or be a superuser
if ($has_access || $is_superuser) {
  // ....
  // do whatever requires access
  // ....
} else die('No access');