      Comparison function for the objects to be inserted in containers. The
            comparison functor must induce a strict weak ordering. Default: <code class="computeroutput"><span class="identifier">compare</span><span class="special">&lt;</span>
            <span class="identifier">std</span><span class="special">::</span><span class="identifier">less</span><span class="special">&lt;</span><span class="identifier">key_type</span><span class="special">&gt;</span>
            <span class="special">&gt