public String handle(String cmd) {
        if (cmd.equals("clear")) {
            cp.clear();
            return "";
        } else if (cmd.startsWith("new")) {
            return handleCreate(cmd);
        } else if (cmd.startsWith("del")) {
            return handleDelete(cmd);
        } else if (cmd.startsWith("con")) {
            return handleConv(cmd);
        }
        return calc.apply(jel, table, cmd);
    }