$members * * @return Set (this set unchanged) */ public function addMulti(array $members): Set { return $this; } /** * Cannot remove members of an immutable set * * @param mixed $x * * @return Set (this set unchanged) */ public function remove($x): Set { return $this; } /** * Cannot remove members of an immutable set * * @param array $x * * @return Set (this set unchanged) */ public function removeMulti(array $x): Set { return $this; } /** * Cannot clear an immutable set * * @return Set (this set unchanged) */ public function clear(): Set { return $this; } }