/// <summary>
        /// Create a merged path.
        /// </summary>
        /// <remarks>
        /// <para>
        /// This method creates an edge path that stops if an edge is not white
        /// or the edge has no more predecessors.
        /// </para>
        /// </remarks>
        /// <param name="se">end edge</param>
        /// <param name="colors">edge color dictionary</param>
        /// <returns>path to edge</returns>
        public EdgeCollection MergedPath(IEdge se, EdgeColorDictionary colors)
        {
            EdgeCollection path = new EdgeCollection();

            IEdge      ec = se;
            GraphColor c  = colors[ec];

            if (c != GraphColor.White)
            {
                return(path);
            }
            else
            {
                colors[ec] = GraphColor.Black;
            }

            path.Insert(0, ec);
            while (EdgePredecessors.Contains(ec))
            {
                IEdge e = EdgePredecessors[ec];
                c = colors[e];
                if (c != GraphColor.White)
                {
                    return(path);
                }
                else
                {
                    colors[e] = GraphColor.Black;
                }

                path.Insert(0, e);
                ec = e;
            }
            return(path);
        }
        /// <summary>
        /// Returns the path leading to the vertex v.
        /// </summary>
        /// <param name="se">end of the path</param>
        /// <returns>path leading to v</returns>
        public EdgeCollection Path(IEdge se)
        {
            EdgeCollection path = new EdgeCollection();

            IEdge ec = se;

            path.Insert(0, ec);
            while (EdgePredecessors.Contains(ec))
            {
                IEdge e = EdgePredecessors[ec];
                path.Insert(0, e);
                ec = e;
            }
            return(path);
        }