href="reference/add_equation.html">add_equation</a></span><span class="op">(</span><span class="st">"H_h = Yd - C_d + H_h[-1]"</span><span class="op">)</span> <span class="op">|&gt;</span> </span>
<span>  <span class="fu"><a href="reference/add_equation.html">add_equation</a></span><span class="op">(</span><span class="st">"Y = C_s + G_s"</span><span class="op">)</span> <span class="op">|&gt;</span> </span>
<span>  <span class="fu"><a href="reference/add_equation.html">add_equation</a></span><span class="op