public LSystem (Axiom a, int iterations)
		{
			this.axiom = a;
			this.iterations = iterations;
			this.rules = new List<Rule> ();
			this.state = new List<Symbol> ();
			state.Add (axiom);
		}
		public LSystem add(Axiom a) {
			this.axiom = a;
			return this;
		}