private List<String> validNegative(List<String> words)
	{
		List<String> tempNumbers = words;
		int negCount = 0;
		while(tempNumbers.contains("negative") || tempNumbers.contains("minus"))
		{
			if(negCount != 0)
			{
				System.err.println("Only one 'negative' or 'minus' allowed");
				System.exit(7);
			}
			else if(tempNumbers.contains("negative"))
			{
				if(tempNumbers.indexOf("negative") != 0)
				{
					System.err.println("negative can only be the first word");
					System.exit(7);
				}
				else
				{
					tempNumbers.remove("negative");
					negCount++;
				}
			}
			else if(tempNumbers.contains("minus"))
			{
				if(tempNumbers.indexOf("minus") != 0)
				{
					System.err.println("minus can only be the first word");
					System.exit(7);
				}
				else
				{
					tempNumbers.remove("minus");
					negCount++;
				}
			}
			negCount++;
		}
		return tempNumbers;
	}