pan><span class="label">sub</span>:string <span class="arrow">&#45;&gt;</span></span>
  <span><span class="label">by</span>:string <span class="arrow">&#45;&gt;</span></span>
  <span>string <span class="arrow">&#45;&gt;</span></span>
  string</span></code></div></div><div class="odoc-spec"><div class="spec value anchored" id="val-is_sub"><a href="#val-is_sub" class="anchor"></a><code><span><span class="keyword">val</span> is_sub : 
  <span><span class="label">sub</span>:string <span class="arrow">&#45;&gt;<