</li>
<li>
	Both types have identical structure and their element types
	unify exactly.
</li>
<li>
	Exactly one type is an <a href="#Type_inference">unbound</a>
	type parameter with a <a href="#Core_types">core type</a>,
	and that core type unifies with the other type per the
	unification rules for <code>≡<sub>A</sub></code>