, for each object of the element type, the object is either considered
to be in the set, or to <em>not</em> be in the set.</p>
<p>Set implementations may consider some elements indistinguishable. These
elements are treated as being the same for any operation on the set.</p>
<p>The default <a href="dart-core/Set-class.html">Set</a> implementation, <a href="dart-collection/LinkedHashSet-class.html">LinkedHashSet</a>, considers objects
indistinguishable if they are equal with regard to
operator <a href="dart-c