b</code> if and only if <code>a == b</code>, but that is not always the
case.  For example, option sets typically do not satisfy that
property.</p>

<p>Two elements are <strong>disjoint</strong> when neither one <em>subsumes</em> the other.</p>

<p><strong>See Also:</strong> <code>OptionSetType</code>.</p>

<ul><li><p>Axioms, where <code>S</code> conforms to <code>SetAlgebraType</code>, <code>x</code> and <code>y</code> are
of type <code>S</code>, and <code>e</code> is of type <code>S.Element</code>:</p><ul