Topological_Sorting

        public void Topological_Sorting()
        {
            var L = new HashSet<Nodo>();

            Action<Nodo> Visit = null;
            Visit = (n) =>
            {
                // if n has a temporary mark then stop (not a DAG)
                if (n.color == Nodo.Color.Gray)
                    throw new Exception("not a DAG!");

                // if n is not marked(i.e.has not been visited yet) then
                if (n.color == Nodo.Color.White)
                {
                    // mark n temporarily
                    n.color = Nodo.Color.Gray;

                    // for each node m with an edge from n to m do visit(m)
                    foreach (var m in Adj[n])
                        Visit(m);

                    // mark n permanently
                    n.color = Nodo.Color.Black;
                    // add n to head of L
                    L.Add(n);
                }
            };

            foreach (var v in V)
                if (v.color == Nodo.Color.White)
                    Visit(v);

            Console.Write("Topological sort: ");
            foreach (var x in L)
                Console.Write(x.N + " ");
            Console.WriteLine();
        }