` append` makes a new list consisting of the members of
its argument lists. ` append` takes any number of arguments.

(append '(a) '(b)) = (a b)(append '(a b) '(c d)) = (a b c d)

(append '(a) '(b) '(c)) = (a b c)

(append '((a b)) '((c d))) = ((a b) (c d))

` reverse` makes a new list that is the reverse of the * top
level* of the list given as its argument.

(reverse '(a b)) = (b a)(reverse '((a b) (c d))) = ((c d) (a b))

` length` returns the length of the top level of
the list given as its argument.

(length '(a)) = 1 (length '(a b)) = 2 (length '((a b))) = 1