private static Set<Trace> checkArgs(String[] args) {
        boolean error = false;
        if (args.length != 2) {
            error = true;
        } else {
            if (args[0].equals("d")) {
                switch (args[1]) {
                    case "L1":
                        return Utils.demoL1eventLog();
                    case "L2":
                        return Utils.demoL2eventLog();
                    case "L7":
                        return Utils.demoL7eventLog();
                    case "LLT":
                        return Utils.demoLLTeventLog();
                    case "chap7":
                        return Utils.chapter7EventLog();

                    default:
                        error = true;
                        break;
                }
            } else if (args[0].equals("f")) {
                return Utils.readInputFromCSV(args[1]);
            } else {
                error = true;
            }
        }
        if (error) {
            usage();
            System.exit(1);
        }
        return new HashSet<>();
    }