NumberList Demo

	    The original list of numbers ...
	    10
	    14
	    7
	    9
	    5
	    6
	    28
	    2
	    1
	    17
	    3
	    >>> help
	    HELP - display a menu of commands
	    DISPLAY - display the list of numbers
	    PRINT - print a number (FIRST;LAST;nth)
	    SWAP - exchange two elements (nth;mth)
	    ADD - add a number to the list (FIRST;LAST)
	    EXIT - terminate execution of the program
	    >>> display
	    10
	    14
	    7
	    9
	    5
	    6
	    28
	    2
	    1
	    17
	    3
	    >>> print first
	    10
	    >>> print last
	    3
	    >>> print 6
	    6
	    >>> print 8
	    2
	    >>> swap 4 9
	    >>> display
	    10
	    14
	    7
	    1
	    5
	    6
	    28
	    2
	    9
	    17
	    3
	    >>> add first 9
	    >>> display
	    9
	    10
	    14
	    7
	    1
	    5
	    6
	    28
	    2
	    9
	    17
	    3
	    >>> add last 23
	    >>> display 
	    9
	    10
	    14
	    7
	    1
	    5
	    6
	    28
	    2
	    9
	    17
	    3
	    23
	    >>> exit