This class is designed to be used as the vertex base class for Triangulation_hierarchy_3.
It inherits from its parameter TriangulationVertexBase_3, and adds the requirements in order to match the concept TriangulationHierarchyVertexBase_3, it does so by storing two Vertex_handles. This design allows to use either a vertex base class provided by CGAL, or a user customized vertex base with additional functionalities.
#include <CGAL/Triangulation_hierarchy_vertex_base_3.h>
It is parameterized by a model of the concept TriangulationVertexBase_3.