pes of iterable may have a different equality used for its elements.
For example, a <a href="dart-core/Set-class.html">Set</a> may have a custom equality
(see <a href="dart-core/Set/Set.identity.html">Set.identity</a>) that its <code>contains</code> uses.
Likewise the <code>Iterable</code> returned by a <a href="dart-core/Map/keys.html">Map.keys</a> call
should use the same equality that the <code>Map</code> uses for keys.</p>
    </section>
    
    <section class="summary source-code" id="source">
      <