hash code represents only the identity of the object,
the same way as the default <a href="models/CardState/operator_equals.html">operator ==</a> implementation only considers objects
equal if they are identical (see <code>identityHashCode</code>).</p>
<p>If <a href="models/CardState/operator_equals.html">operator ==</a> is overridden to use the object state instead,
the hash code must also be changed to represent that state.</p>
<p>Hash codes must be the same for objects that are equal to each other
accord