/span> <span class="identifier">base_types</span><span class="special">;</span> <span class="comment">// For subcontracting.</span>
    <span class="preprocessor">#undef</span> <span class="identifier">BASES</span>

    <span class="keyword">void</span> <span class="identifier">invariant</span><span class="special">()</span> <span class="keyword">const</span> <span class="special">{</span> <span class="comment">// Checked in AND with base class invariants.</span>
        <span class="identifier">BOOST_CONTR