append

append &rest lists → result

list — each must be a proper list except the last, which may be any object.

result — an object. This will be a list unless the last list was not a list and all preceding lists were null.

append returns a new list that is the concatenation of the copies. lists are left unchanged; the list structure of each of lists except the last is copied. The last argument is not copied; it becomes the cdr of the final dotted pair of the concatenation of the preceding lists, or is returned directly if there are no preceding non-empty lists.

(append '(a b c) '(d e f) '() '(g)) → (A B C D E F G) 
(append '(a b c) 'd) → (A B C . D) 
(setq lst '(a b c)) → (A B C) 
(append lst '(d)) → (A B C D) 
lst → (A B C) 
(append) → NIL 
(append 'a) → A

nconc, concatenate