edge list structure the edge list structure is possibly the simplestthough not the most efficientrepresentation of graph all vertex objects are stored in an unordered list and all edge objects are stored in an unordered list we illustrate an example of the edge list structure for graph in figure (ah (bfigure (aa graph (bschematic representation of the edge list structure for notice that an edge object refers to the two vertex objects that correspond to its endpointsbut that vertices do not refer to incident edges to support the many methods of the graph adt (section )we assume the following additional features of an edge list representation collections and are represented with doubly linked lists using our positionallist class from vertex objects the vertex object for vertex storing element has instance variables fora reference to element xto support the elementmethod reference to the position of the vertex instance in the list thereby allowing to be efficiently removed from if it were removed from the graph edge objects the edge object for an edge storing element has instance variables fora reference to element xto support the elementmethod references to the vertex objects associated with the endpoint vertices of these allow the edge instance to provide constant-time support for methods endpointsand opposite(va reference to the position of the edge instance in list ethereby allowing to be efficiently removed from if it were removed from the graph