ass="arrow">&#45;&gt;</span></span> <span><a href="#type-expr">expr</a> <span class="arrow">&#45;&gt;</span></span> <a href="#type-expr">expr</a></span></code></div><div class="spec-doc"><p><code>subst_id phi e</code> applies substitution <code>phi</code> to expression <code>e</code>, substituting each occurrence of identifier <code>id</code> by identifier <code>phi id</code></p></div></div><div class="odoc-spec"><div class="spec value anchored" id="val-subst_lval"><a href="#val-subst_lval" class="anchor"><