public static String processCommand(ArrayList<String> commandArray, ArrayList<City> cities, ArrayList<Mines> mines) {
		String expression = null;

		if (commandArray.get(0).toLowerCase().equals("feed") && commandArray.size() == 5) {
			expression = processFeed(commandArray, cities, mines);
		} else if (commandArray.get(0).toLowerCase().equals("transfer") && commandArray.size() == 7) {
			expression = processTransfer(commandArray, cities, mines);
		} else if (commandArray.get(0).toLowerCase().equals("build") && commandArray.size() == 5) {
			expression = processBuild(commandArray, cities, mines);
		} else if (commandArray.get(0).toLowerCase().equals("help") && commandArray.size() == 1) {
			processHelp();
		} else if (commandArray.get(0).toLowerCase().equals("quit")) {
			processQuit();
		} else {
			expression = invalid;
		}
		
		return expression;
	}