w">&#45;&gt;</span></span> <span><a href="#type-subst">subst</a> <span class="arrow">&#45;&gt;</span></span> <a href="#type-subst">subst</a> * <a href="#type-subst">subst</a> * <a href="#type-subst">subst</a></span></code></div><div class="spec-doc"><p>Compute the common id-exp part of two inputs <code>subst1</code> and <code>subst2</code>. The first component of the output is this common part. The second and third components are the remainder of <code>subst1</code> and <code>subst2</code>, respectively.</p