@Override
 public Value apply(Spreadsheet s, List<Expression> args) {
   if (args.size() == 0) {
     System.out.println(HelpSystem.mainHelpMessage());
   } else if (args.size() == 1) {
     System.out.println(
         HelpSystem.helpMessage(((pw.qxczv.TextExcel.AST.Identifier) (args.get(0))).nm));
   }
   return null;
 }