ss="special">&amp;</span> x<span class="special">,</span> <span class="keyword">const</span> <span class="identifier">state_type</span> <span class="special">&amp;</span> x_old<span class="special">,</span> 
                <span class="identifier">time_type</span> t_old<span class="special">,</span> <span class="keyword">const</span> <span class="identifier">state_type</span> <span class="special">&amp;</span> x_new<span class="special">,</span> <span class="identifier">time_type</span> t_new<span class="s