ecial">,</span> <span class="keyword">const</span> <span class="identifier">state_type</span> <span class="special">&amp;</span> x<span class="special">,</span> <span class="identifier">time_type</span> t<span class="special">,</span> 
               <span class="identifier">state_type</span> <span class="special">&amp;</span> xout<span class="special">,</span> <span class="identifier">time_type</span> dt<span class="special">,</span> <span class="identifier">state_type</span> <span class="special">&amp;</s