sts,
      pipes etc.
    </p>
<h4>
<a name="coroutine.intro.h3"></a>
      <span class="phrase"><a name="coroutine.intro.execution_transfer_mechanism"></a></span><a class="link" href="intro.html#coroutine.intro.execution_transfer_mechanism">execution-transfer
      mechanism</a>
    </h4>
<p>
      Two categories of coroutines exist: symmetric and asymmetric coroutines.
    </p>
<p>
      An asymmetric coroutine knows its invoker, using a special operation to implicitly
      yield control specifically to 