/code> applies the renaming <code>f</code> to identifiers in the domain of <code>sub</code> and the substitution <code>g</code> to the expressions in the range of <code>sub</code>.</p></div></div><div class="odoc-spec"><div class="spec value" id="val-extend_sub" class="anchored"><a href="#val-extend_sub" class="anchor"></a><code><span><span class="keyword">val</span> extend_sub : <span><a href="#type-subst">subst</a> <span class="arrow">&#45;&gt;</span></span> <span><a href="../../IR/Ident/index.html#type-t