unification depending on whether two types have to be
<a href="#Type_identity">identical</a>,
<a href="#Assignability">assignment-compatible</a>, or
only structurally equal.
The respective <a href="#Type_unification_rules">type unification rules</a>
are spelled out in detail in the <a href="#Appendix">Appendix</a>.
</p>

<p>
For an equation of the form <code>X ≡<sub>A</sub> Y</code>,