PURE is an object-oriented system implemented in C++.
In order to be able to keep epilogue objects on a queue,
the class implementing an epilogue is inherited from a base
class that provides queuing capability. This base class,
Chain, is providing a next pointer to support the implementation
of single-linked lists. The head of this list then is
implemented by a single Chain* instance. Extending the
list head by a second Chain* instance which implements
the pointer to the last list element (i.e. the tail) results in a
queue. The resulting class is shown in Figure 3.