reverse

reverse takes one list, and returns a new list with the same elements in the opposite order. For example,

(reverse '(1 2 3 4))

returns a list (4 3 2 1). Like append only reverses the top-level structure of the list it's given.

(reverse '((1 2) (3 4)))

returns ((3 4) (1 2)), not ((4 3) (2 1))