&lt;</span><span class="keyword">typename</span> System<span class="special">&gt;</span> 
  <span class="keyword">void</span> <a name="idp20529536-bb"></a><span class="identifier">do_step</span><span class="special">(</span><span class="identifier">System</span> system<span class="special">,</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">,<