i>Empire, Map, Unit, ForeignUnitList, Model, ForeignModel, City, ForeignCity, Blueprint, Negotiation, Persistent</i>. Also, don't remove them from their collection. These objects are managed by existing code.
</p>

<p>
Be aware that units and cities might stop to exist. If you're still referring the connected object then, it will tell its property <i>Exists</i> as false.
</p>


<h2>Identity of Items</h2>

<p>
You can use == with all refernce types for identity check because there are never two different ins