" id="val-sub_empty" class="anchored"><a href="#val-sub_empty" class="anchor"></a><code><span><span class="keyword">val</span> sub_empty : <a href="#type-subst">subst</a></span></code></div><div class="spec-doc"><p>The empty substitution.</p></div></div><div class="odoc-spec"><div class="spec value" id="val-is_sub_empty" class="anchored"><a href="#val-is_sub_empty" class="anchor"></a><code><span><span class="keyword">val</span> is_sub_empty : <span><a href="#type-subst">subst</a> <span class="arrow">&#45;&g