class="pln">isBtlForwardRange</span><span class="pun">!</span><span class="pln">R </span><span class="pun">&amp;&amp; </span><span class="kwd">is</span><span class="pun">(</span><span class="kwd">typeof</span><span class="pun">((</span><span class="pln">R r</span><span class="pun">) =&gt; </span><span class="pln">r<wbr/></span><span class="pun">.</span><span class="pln">popBack</span><span class="pun">)) &amp;&amp; </span><span class="kwd">is</span><span class="pun">(</span><span class="typ">ReturnType</spa