Numbers, Lists inside of Lists
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Lists can also have numbers in them, as in this list: `(+ 2 2)'.
This list has a plus-sign, `+', followed by two `2's, each separated by
whitespace.
In Lisp, both data and programs are represented the same way; that
is, they are both lists of words, numbers, or other lists, separated by
whitespace and surrounded by parentheses. (Since a program looks like
data, one program may easily serve as data for another; this is a very
powerful feature of Lisp.) (Incidentally, these two parenthetical
remarks are _not_ Lisp lists, because they contain `;' and `.' as
punctuation marks.)
Here is another list, this time with a list inside of it:
'(this list has (a list inside of it))
The components of this list are the words `this', `list', `has', and
the list `(a list inside of it)'. The interior list is made up of the
words `a', `list', `inside', `of', `it'.