</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, and all the types in its type set unify with
	the other type
	per the unification rules for <code>≡<sub>A</sub></code>
	(loose unification at the top level and exact unification