="identifier">multiply_action</span> <span class="special">&gt;</span><span class="special">,</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">units</span><span class="special">::</span><span class="identifier">unit</span><span class="special">&lt;</span> <span class="identifier">Dim1</span><span class="special">,</span> <span class="identifier">System1</span> <span class="special">&gt;</span><span class="special">,</span> <span class="identifier">boost</sp