/*!  \~english
 * ... text ...
 * The distance between \f$(x_1,y_1)\f$ and \f$(x_2,y_2)\f$ is
		\f$\sqrt{(x_2-x_1)^2+(y_2-y_1)^2}\f$.
 * @htmlonly
 *  <div class="mermaid">
 * sequenceDiagram
 *    Alice->>John: Hello John, how are you?
 *    loop Healthcheck
 *        John->>John: Fight against hypochondria
 *    end
 *    Note right of John: Rational thoughts!
 *    John-->>Alice: Great!
 *    John->>Bob: How about you?
 *    Bob-->>John: Jolly good!
 *  </div>
 *  <script src="https://unpkg.com/mermaid/dist/mermaid.min.js"></script>
 *  <script>mermaid.initialize({startOnLoad:true});</script>
 * @endhtmlonly
 */