span class="special">&gt;</span><span class="special">,</span> <span class="keyword">void</span> <span class="special">&gt;</span><span class="special">::</span><span class="identifier">type</span> 
  <a name="idp20661200-bb"></a><span class="identifier">do_step</span><span class="special">(</span><span class="identifier">System</span> system<span class="special">,</span> <span class="identifier">StateInOut</span> <span class="special">&amp;</span> x<span class="special">,</span> <span class="keyword">const