If You're Good With Arrays And Lists, This One's For You

I'm using PHP 4.4.4. Let's say I have two scalars, $list1 and $list2.
Both are comma separated lists of ordered, unsigned, unique integers.
An example would be

$list1 = "2,26,345";
$list2 = "3,4,26,35,525";

I am wondering if there is a short way of determining if all the
numbers in $list1 occur in $list2.