8</span>&#160; </div>
<div class="line"><a name="l00019"></a><span class="lineno">   19</span>&#160;<span class="preprocessor">#include &quot;absl/types/optional.h&quot;</span></div>
<div class="line"><a name="l00020"></a><span class="lineno">   20</span>&#160;<span class="preprocessor">#include &quot;<a class="code" href="linear__solver_8pb_8h.html">ortools/linear_solver/linear_solver.pb.h</a>&quot;</span></div>
<div class="line"><a name="l00021"></a><span class="lineno">   21</span>&#160;<span class="prep