    <tr>
            <td style="font-family: Courier New,Courier,monospace;">bool
            <span style="font-weight: bold;">is_linear</span>() const </td>
            <td>Returns true if the edge
is linear (segment, ray, line), else false. </td>
          </tr>
          <tr>
            <td style="font-family: Courier New,Courier,monospace;">bool
            <span style="font-weight: bold;">is_curved</span>() const </td>
            <td>Returns true if the edge
is curved (parabolic arc), else false. </t