private boolean isNumber(String st) {
		if (st.charAt(0) == Tokenizer.minusSign && st.length() == 1)
			return false;
		for (char ch : st.toCharArray()) {
			if (!Character.isDigit(ch) && ch != Tokenizer.minusSign && ch != Tokenizer.decimalSeparator)
				return false;
		}
		return true;
	}