lass="keyword">struct</span> <span class="identifier">is_dimensionless_unit</span><span class="special">&lt;</span> <span class="identifier">unit</span><span class="special">&lt;</span><span class="identifier">dimensionless_type</span><span class="special">,</span><span class="identifier">System</span><span class="special">&gt;</span> <span class="special">&gt;;</span>
<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">System</sp