It is a string of characters beginning with a letter, digit or special character other than left "(" or right ")" parentheses.
Examples::
Peace
of
Mind
9518
3.1416
It is a collection of S-Expression enclosed by parentheses.
Examples:
(The 100 capital sins)
(3.1416 ((peach) oranges) apricot)
It is a special S-Expression that is both an atom and a list.
Example:
()
In order to make the difference between a list and a
function Invocation, we have to begin
the list with the quote sign '.(see
function definition)
