But why? What would that make easier? A list is defined as a directed graph where each node has one vertex in each direction. That definition works equally w

But why? What would that make easier? A list is defined as a directed graph where each node has one vertex in each direction. That definition works equally well for existing languages, e.g. struct Node { struct Node *prev, *next; int payload; }: The types gives you some constraints on the shape of the graph.