public void accept(GrammarNodeV_Visitor visitor)
 {
     startSymbol.accept(visitor);
 }
 public override void accept(GrammarNodeV_Visitor visitor)
 {
     visitor.visit(this);
 }
 //internal abstract void ExpandAllNonterminalsOnce(List<NonterminalHeadD> seen);
 public abstract void accept(GrammarNodeV_Visitor visitor);