private List<String> verifyBracketTokens(List<String> tokens) throws ParserException {
		List<String> newTokens = new ArrayList<String>();
		int bracketType = -1;
		String[] brackets = null;
		for (int i = 2; i < tokens.size() && bracketType < 0; i++) {
			if (!"".equals(tokens.get(i))) bracketType = i;
		}
		switch (bracketType) {
		case 2:
			brackets = new String[] { "$", "$" };
			break;
		case 3:
			brackets = new String[] { "(", ")" };
			break;
		case 4:
			brackets = new String[] { "[", "]" };
			break;
		case 5:
			brackets = new String[] { "{", "}" };
			break;
		default:
			return null;
		}
		String tokenString = tokens.get(bracketType);
		newTokens.add(brackets[0]);
		newTokens.add(tokenString);
		newTokens.add(brackets[1]);
		return newTokens;
	}