r">quantity</span><span class="special">&lt;</span><span class="identifier">Unit1</span><span class="special">,</span><span class="identifier">Y</span><span class="special">&gt;</span></code> and <code class="computeroutput"><span class="identifier">quantity</span><span class="special">&lt;</span><span class="identifier">Unit2</span><span class="special">,</span><span class="identifier">Z</span><span class="special">&gt;</span></code> is allowed if <code class="computeroutput"><span class="identifier">Unit1