b</span>
<span class="w">         </span><span class="n">z</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">t</span>
<span class="w">         </span><span class="n">t</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">d</span><span class="p">(</span><span class="n">i</span><span class="p">)</span><span class="o">*</span><span class="n">t</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span 