private String getExpression(int index) throws SyntaxErrorException {
		int c = 1;
		for (int j = index + 1; j < expression.length(); j++) {
			char s = expression.charAt(j);
			if (s == '(')
				c++;
			if (s == ')')
				c--;
			currentPosition = j;
			if (c == 0)
				return expression.substring(index + 1, j);
		}
		throw new SyntaxErrorException(
				Tools.getLocalizedString("MISSING_BRACKETS"), index);
	}