public static Edge_speedway CreateEdge(LGSPGraph graph, LGSPNode source, LGSPNode target)
        {
            Edge_speedway edge = new Edge_speedway(source, target);

            graph.AddEdge(edge);
            return(edge);
        }
		public static Edge_speedway CreateEdge(LGSPGraph graph, LGSPNode source, LGSPNode target)
		{
			Edge_speedway edge = new Edge_speedway(source, target);
			graph.AddEdge(edge);
			return edge;
		}