Lisp S-Expressions: Lists
We define lists as follows:
The symbol NIL is a list; it’s the empty list.
This list is written in list notation as ( )
Any cons having the following structure is a list,
(S1 . (S2 . ( ... (Sn . NIL) ... ) ) )
where each S1 is either an atom or a cons.
This list is written in list notation as