l">=</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">contract</span><span class="special">::</span><span class="identifier">function</span><span class="special">()</span>
        <span class="special">.</span><span class="identifier">precondition</span><span class="special">([&amp;]</span> <span class="special">{</span>
            <span class="identifier">BOOST_CONTRACT_ASSERT</span><span class="special">(</span><span class="identifier">x</span> <span cla